Extra armed police will be deployed at major events across London in the wake of the Manchester suicide bombing, the Metropolitan Police has confirmed.
The force has also increased the number of officers on duty across the capital in response to the terror attack at an Ariana Grande concert, which left at least 22 dead and 59 injured.
Additional armed officers will police the FA Cup final at Wembley between Arsenal and Chelsea as well as the Rugby Premiership final between Wasps and Exeter Chiefs at Twickenham Stadium on Saturday 27 May.
"Here in London we are determined to do all we can to protect the capital," said Metropolitan Police commander Jane Connors.
"That means that over the coming days as you go to a music venue, go shopping, travel to work or head off to the fantastic sporting events you will see more officers - including armed officers.
"As the full horror of last night's attack in Manchester still sinks in the thoughts of all of us in the Met Police are with those who have lost loved ones or who were injured.
"We are used to delivering policing operations that seek to mitigate against the severe threat we face from terrorists. It is only right that we now take time to review those existing plans and make sure we are confident that we are doing all we can.
"As you are out and about in London please be alert – call us immediately if you see something suspicious. If you are at an event and something worries you, go straight to a police officer or security guard and tell them."
The national threat level has been raised from "severe" to "critical" by the Joint Terrorism Analysis Centre (JTAC). The move means "an attack is expected imminently" and the Army can deploy up to 5,000 troops across the UK.
"I want to reassure all Londoners and visitors that we are doing everything possible to protect our city," said Mayor of London Sadiq Khan.
"As your Mayor, I am in constant contact with the Metropolitan Police and we are liaising closely with the Government and security services.
"Our emergency services prepare day in, day out for these situations. Our plans are well rehearsed and well prepared. I would urge all Londoners and visitors to remain calm and vigilant, and to report anything suspicious to the police.
"There will be additional police officers on London's streets over the coming days - including additional armed officers. You will also see some military personnel around London - they are there to help our police service to keep us safe and guard key sites."