David Cameron has pledged that the UK will do "all we can to help" after Tunisia, France and Kuwait were rocked by a spate of terror attacks on 26 June.
The prime minister also called an emergency meeting of the Cobra committee, a cabinet discussion led by the Home Secretary, Theresa May, to plan Britain's domestic response to the major crises.
Cameron, speaking in Brussels, brandished the attacks as "appalling terrorist acts" and said "our hearts go out to the victims".
"I am sickened by the attacks in Tunisia, France and Kuwait. Our countries stand together in combating the horrors of terrorism," the prime minister said in a separate statement on Twitter.
Cameron issued the comments after at least 27 people were killed when two gunmen attacked a beach resort in Sousse, Tunisia.
A British holidaymaker, who was caught up in the assault, gave a harrowing account of the assault to IBTimes UK.
"We had just played a game of volleyball and then I went off into the sea, 20-30 yards out from the shore," he said.
"I turned and heard gunshots and then saw a splattering of gunshots hit the ground.
"As soon as I turned around I saw one older gentleman hit in the side of his head and he dropped straight down, then there were two large explosions."
The attack happened after a man was decapitated in what appears to be a terror attack near Lyon, France.
Islamist flags were discovered at the scene in Saint-Quentin-Fallavier and the victim's head was found on a post outside of the US-owned Air Products gas factory.
French interior minister Bernard Cazeneuve named one of the alleged attackers as Yassine Salim, who was already known to the French authorities, and revealed that the other suspect was shot dead by police.
Elsewhere, an Islamic State (Isis) affiliated group claimed responsibility for a suicide bomb attack on a Shia Mosque in Kuwait. The assault left at least 10 worshippers dead and dozens of people injured.