Salman Abedi killed 22 people, some of them children, when he detonated a bomb in the foyer of Manchester Arena at an Ariana Grande concert on 22 May.
The government raised the threat level from "severe" to "critical" and launched Operation Temperer, deploying armed officers at airports, stations and sports venues around UK, after the terror attack.
Prime Minister Theresa May branded the suicide bombing "a callous and cowardly terrorist attack" that targeted "innocent children, young people and their families."
Sixty-four people were injured in the attack. Twelve of them were under the age of 16.
The victims of the attack include an 8-year-old girl, two teenagers and a Polish couple.
Here are those of the 22 victims who have been named so far.
Martyn Hett, 29
Stockport-born Martyn Hett was a Coronation Street superfan with a distinctive tattoo of character Deirdre Barlow on his ankle.
The PR manager was once a winner of the television competition Come Dine with Me and also appeared on the show Tattoo Fixers.
His heartbroken partner, Russell Hayward, shared an emotional tribute to Hett on social media.
"He left the world exactly how he lived, centre of attention. I'm in a really bad way so please forgive if I don't reply. Thankfully I have his wonderful and amazing friends to keep each other strong. I love you Martyn. I always will," he wrote on Twitter.
He also shared a picture of Hett embracing him and wrote: "Soulmate doesn't even come close. Come back to us Martyn so we can watch last nights Corrie together."
Angelika and Marcin Klis, 40 and 42
Polish couple Marcin, a cab driver for York Car Taxi Service, and Angelika, were picking their two daughters up from the Ariana Grande concert when the bomb went off.
Their daughter Alex, an 18-year-old student at York University, shared a picture of her parents on Facebook, asking people with information to come forward. Her post was shared more than 12,000 times.
The Polish foreign ministry confirmed on Tuesday (23 May) that the couple had died in the attack. Family members from Poland have travelled to the UK to support Alex and her sister Patricia.
Kelly Brewster, 32
Brewster, who worked for Irwin Mitchell Solicitors in Sheffield, was at the Manchester Arena with her sister Claire and niece Hollie when the bomb detonated.
Her uncle, Paul Dryhurst, said his niece had "heroically shielded" 11-year-old Hollie from the shrapnel in the foyer. Brewster's partner, Ian Winslow, confirmed her death in a Facebook post.
"Kelly Brewster wasn't one of the unidentified hospital patients. She has sadly passed away in the terror attack yesterday," he wrote. "Kelly really was the happiest she has ever been and we had so many things planned together. My daughter Phoebe will be absolutely devastated like we all are."
Olivia Campbell, 15
15-year-old schoolgirl Olivia Campbell, from Bury in Greater Manchester, died in the explosion.
Her mother, Charlotte Campbell, launched an appeal for her daughter when she could not get in touch with her after the concert. She appeared on ITV's Good Morning Britain and moved the presenters to tears as she said that she hadn't spoken to Olivia since she set off for the concert.
She wrote a moving tribute to her daughter on Facebook: "RIP my darling precious gorgeous girl Olivia Campbell taken far far too soon go sing with the angels and keep smiling mummy loves you so much."
Lisa Lees, 47
The mother from Royton, Oldham, was waiting for her 15-year-old daughter in the foyer of Manchester Arena when the bomb exploded.
Her stepson, Jordan Howe, confirmed her death on Facebook: "They took a caring beautiful mum and step mother away from us all she was amazing to us all love you loads Alison Howe xx."
Her brother, Lee Hunter, also shared the news on social media: "For those who don't know Lisa is gone but never, ever forgotten. I love you Lisa I'll miss you so much."
Alison Howe, 45
Howe was with her friend Lees at the time of the explosion. She was also waiting for her teenage daughter to emerge from the concert venue. Both their daughters were not injured in the attack.
Friend Sarah Parker paid tribute to the Oldham mother: "Alison Howe was the first person to talk to me and make me feel welcome when Sisley started dancing with Darcey. You were gorgeous wonderful woman," she said.
"The only condolence is your beautiful girls are safe and you'd of done anything for that. Broken hearted and cannot begin to understand your family's pain."
Saffie Rose Roussos, 8
The youngest victim to be named so far, Saffie Rose Rousos was a primary school student from Leyland, Lancashire.
Her mother, Lisa, and older sister Ashlee are reported to be in hospital with non-life threatening injuries. Her parents are believed to run a fish and chip shop in Leyland.
The headteacher at her school, Chris Upton, described her as a "beautiful little girl in every aspect of the word" and a "quiet and unassuming student with creative flair."
"She was loved by everyone and her warmth and kindness will be remembered fondly," Upton said.
John Atkinson, 26
26-year-old Atkinson lost his life in the terrorist attack. The pop fan from Radcliffe was a competitive dancer for a local adult dance troupe, Freak Dance Radcliffe.
On the group's Facebook page a message read: "Today is an amazingly sad day! We have lost a member of our dance family."
They described him as a "happy gentle person" and a "real pleasure to teach."
Tracey Crolla wrote on Facebook: "Thinking of all the Atkinsons at this very sad time. John Atkinson you turned into an amazing young man so kind and thoughtful you will be missed by everyone x x."
Friends set up a fundraising page for Atkinson's family, which has so far raised more than £4,500.
Georgina Callander, 18
The first named victim of the attack, 18-year-old Georgina Callander was an Ariana Grande superfan who was incredibly excited to see her idol perform in Manchester.
Before the concert on Monday, Callander tweeted the singer: "SO EXCITED TO SEE YOU TOMORROW."
After meeting Grande in 2015, the school student from Lancashire shared a picture of her smiling broadly next to the pop singer with the caption: "Thank you for everything my love I miss you."
Jane Tweddle-Taylor, 50
Tweddle-Taylor, a receptionist at South Shore Academy School in Blackpool, was waiting for a friend who was picking up her daughter from the concert when the blast occurred.
Wayne Wareing paid tribute to her: "We had some laughs when I came into school for Richard," he said. "You always seemed to make me walk out laughing when I came in raging. You had a big heart and a loveable character. My thoughts are with everyone that lost someone in Manchester."
The schoolgirl attended the Ariana Grande concert with her brother, who is in hospital with serious injuries.
Helen McDermott, from Halewood in Merseyside, set up a fundraising page to raise money for a "beautiful send off for Megan who was taken far too early."
When donations reached the initial target of £500, McDermott thanked everyone for their generosity. "Can not believe the response of our wonderful Halewood/Liverpool locals and anyone else who has donated so far!! So heartwarming in such a gut wrenching situation!! The family must be beside themselves," she wrote on the fundraising page.
A service was held on Tuesday evening (23 May) at St Nicholas' Church in Halewood for Hurley and other victims of the explosion.
Nell Jones, 14
14-year-old schoolgirl Nell Jones died in the bombing. Her form tutor, David Wheeler, described Jones as a "very popular girl, always smiling, always positive."
"Her tutor group have been together since the transition from primary school. It feels like they have lost a sister not a classmate," he said.
Michelle Kiss, 45
Michelle Kiss is the mother of the young girl who was pictured being comforted by a police office outside the Manchester Arena in the wake of the attack.
The family have now confirmed the mother-of-three died from her injuries. They said in a statement: "Michelle Kiss was a loving wife to Tony, mother to Dylan, Elliot and Millie, as well as daughter to Mick and Christine and sister to Nichola.
"Family was her life and we are all obviously devastated by her loss. She has been taken away from us, and all that love her, in the most traumatic way imaginable.
"We hope to draw from the courage and strength she showed in her life to get through this extremely difficult time."
Eilidh MacLeod, 14
Eilidh MacLeod, celebrating her birthday, travelled from Outer Hebrides with her friend Laura Macintyre to attend the concert. Eilidh was killed in the blast, while Laura suffered severe injuries and is now in hospital.
Eilidh's parents issued a statement: "Our family is devastated and words cannot express how we feel at losing our darling Eilidh. Eilidh was vivacious and full of fun. She loved all music whether it was listening to Ariana or playing the bagpipes with her pipe band. As a family we would like to express our thanks and gratitude for the support and kind messages we have received at this difficult time."
Police officer Elaine McIver
Off-duty police officer Elaine McIver was among those killed at Manchester Arena in the bombing of the Ariana Grande concert. The detective constable was attending the concert with her husband Paul and their two children. All three were also injured in the blast.
Cheshire Police, the force she served with, confirmed her death on Wednesday but declined to provide further details.
The family statement: "Elaine was a much loved daughter, sister, auntie, friend and colleague, the best we could ever have wished for. She was everyone's friend, thoughtful beyond belief with an effervescent and outgoing personality. She would have been devastated by the injuries sustained by her partner Paul, and we all wish him a speedy recovery.
"Elaine just loved life, and had a major love of music. Despite what has happened to her, she would want us all to carry on regardless and not be frightened by fear tactics, instead she regularly urged us all to rise up against it.
"Although we will all miss her beyond belief, we absolutely know she will live in our hearts forever."
Wendy Fawell, 50
Wendy Fawell, a mother from Otley in West Yorkshire, was collecting her daughter from the Ariana Grande concert when the explosion took place.
Confirming the news, a friend, Debbie Mcdowell wrote on Facebook: "I am heartbroken beyond belief. I have lost my best friend and confident Wendy Fawell. A beautiful, lady who I will have treasured memories of. Nite god bless sweetheart. Love you to the moon and back xxxx."
Staff at the primary school where she worked have expressed their "deep sadness" over her death.
On Thursday, St Oswald's C of E Primary School, in Guiseley, said on Twitter: "It is with deepest sadness that I confirm that our former colleague Wendy Fawell was killed in the Manchester bombing. RIP, Wendy."
Greg Mulholland, the Liberal Democrat candidate standing in Leeds North West, wrote on Facebook: "Heartbreaking that Wendy Fawell has been confirmed as a victim of the Manchester attack, deepest condolences, thoughts and prayers with her family and friends."
Sorrell Leczkowski, 14
Sorrell Leczkowski from Leeds, a year 9 student at Allerton High School, was attending the concert with her mother and grandmother when they were all struck by the blast. Sorrell was confirmed dead on Wednesday. Her mother and grandmother survived and are being treated for injuries.
Sorrell's Grandfather told Metro: "Sorrell was only 14, but she was our rock, she kept us all grounded."
Courtney Bolye, 19, and stepfather Philip Tron, 32
19-year-old Courtney Boyle had travelled form Gateshead with her stepfather Philip Tron, 32, to attend the concert at the Manchester Arena.
In a statement, Courtney's mum said: "My stunning amazing beautiful daughter you were my rock you made me so proud with all you had achieved and my gorgeous crazy Philip you made my world a happy place and now you are both my angels flying high in the sky."
Tron' s family added: Firstly, we would like to thank the emergency services, police, nurses, support staff, family & friends and the people of Manchester for their continued help and support which they have given us throughout this harrowing time.
"Our most amazing son, partner, brother, father, uncle, nephew and cousin, Philip Tron, sadly passed away on the 22nd May 2017.
Philip was such a fun loving, energetic soul, he would light up the darkest room and lift your spirits with his infectious laugh, witty sense of humour and his beautiful smile."
Liam Curry, 19, and Chloe Rutherford, 17
A young and "Inseparable" couple form South Shield were also killed in the attack.
A joint statement from the pair's families was released. It said: "On the night our daughter Chloe died and our son Liam died, their wings were ready but our hearts were not.
"They were perfect in every way for each other and were meant to be. They were beautiful inside and out to ourselves and our families, and they were inseparable.
"Chloe always described herself as ditzy who Liam adored and would do anything for, including dealing with Chloe's demands for chocolate.
"They lived to go to new places together and explore different cities. They wanted to be together forever - and now they are."