Leaders in the U.K. increased the country's terror threat level following the attack Monday at the Manchester Arena. British Prime Minister Theresa May says it is a "proportionate and sensible response" to the suicide bombing.
Police in the UK arrested a 23-year-old man in Manchester early Tuesday in connection with the terrorist attack that took at least 22 lives Monday night.
The Islamic State group says one of its members carried out the attack. The bombing rocked the country, underscoring the ongoing terrorist threat to Europe.
At least 22 people were killed and 59 others wounded by the explosion which took place at an Ariana Grande concert in Manchester in northern England.
The bombing happened just after the American pop singer was closing a show at the Manchester Arena.
Authorities say many children are among the victims, including an 8-year-old girl, Saffie Roussos, who was killed in the bombing.
Chaos and confusion sent concertgoers, many of them children, screaming and scrambling for the exits.
"We just started running, there was a lot of screaming and crying," one survivor said.
Grande had just gotten off the stage when the explosion rocked the building.
"We believe the attacker was carrying an improvised explosive device which he detonated causing this atrocity," Manchester Police Chief Constable Ian Hopkins said.
Grande took to Twitter to offer condolences to the victims and her fans saying, "Broken. From the bottom of my heart, I am so sorry. I don't have words."
Manchester Mayor Andy Burnham said the city woke up to the most difficult of dawns following the bombing.
"It is hard to believe what has happened here in the last few hours and to put into words the shock, anger and hurt that we feel today. These were children, young people and their families that those responsible chose to terrorize and kill. This was an evil act," Burnham said.
Speaking in Bethlehem in Israel during his first foreign trip since he took office, President Donald Trump called the attacker an "evil loser."
"As president of the United States, on behalf of the people of the United States, I would like to begin by offering my prayers to the people of Manchester in the United Kingdom. I extend my deepest condolences to those so terribly injured in this terrorist attack and to the many killed and the families, so many families of the victims," he said.
Trump said the bombing underscored the message he had delivered over the past several days about the need to confront terrorism.
"This is what I've been these last few days talking about during my trip overseas. Our society can have no tolerance for this continuation of bloodshed. We cannot stand a moment longer for the slaughter of innocent people and in today's attack it was mostly innocent children," Trump said.
Meanwhile, Islamic State supporters celebrated on social media Tuesday after the concert blast in Manchester.
Tweets from Islamic extremists were posted hours before the attack.
One tweet said: "Are you forget our threat? This is the just terror."
Another tweet read: "We have more."
Multiple Islamic State accounts were suspended from Twitter where each was using the hashtag #ManchesterArena.
Britain's terrorist threat level has been set at "severe" in recent years, indicating an attack is highly likely. Police said they're working with counter-terrorism officers, who say they're averaging one arrest a day of terrorism suspects, and intelligence agencies.