Photos: Deadly explosion at Ariana Grande concert People in Manchester, England, gather in St. Ann's Square on Thursday, May 25. They were observing a national minute of silence to remember the victims of a suicide bombing at an Ariana Grande concert. Hide Caption 1 of 22

Photos: Deadly explosion at Ariana Grande concert Britain's Queen Elizabeth II speaks to 15-year-old Millie Robson and her mother, Marie, during a visit to the Royal Manchester Children's Hospital on May 25. The Queen was visiting those injured in the attack. Hide Caption 2 of 22

Photos: Deadly explosion at Ariana Grande concert A police officer guards a house in Manchester as investigations continued on May 25. Police say a man carrying explosives acted as a lone attacker and died in the blast. Hide Caption 3 of 22

Photos: Deadly explosion at Ariana Grande concert Flowers and tribute messages are left for victims in St. Ann's Square. Hide Caption 4 of 22

Photos: Deadly explosion at Ariana Grande concert A women sheds tears after observing the minute of silence in St. Ann's Square. Hide Caption 5 of 22

Photos: Deadly explosion at Ariana Grande concert A Manchester road is closed off as police raids continued on May 25. Hide Caption 6 of 22

Photos: Deadly explosion at Ariana Grande concert Local residents hold Manchester City and Manchester United soccer jerseys during the national minute of silence. Hide Caption 7 of 22

Photos: Deadly explosion at Ariana Grande concert Police officers deliver flowers to a makeshift memorial in Manchester on Wednesday, May 24. Hide Caption 8 of 22

Photos: Deadly explosion at Ariana Grande concert Women cry after placing flowers in Manchester on May 24. Hide Caption 9 of 22

Photos: Deadly explosion at Ariana Grande concert A forensics team works at the scene of the explosion on Tuesday, May 23. Hide Caption 10 of 22

Photos: Deadly explosion at Ariana Grande concert British Prime Minister Theresa May condemns the "callous terrorist attack" as she delivers a statement in London on May 23. Hide Caption 11 of 22

Photos: Deadly explosion at Ariana Grande concert Police help someone after the attack at Manchester Arena on Monday, May 22. Hide Caption 12 of 22

Photos: Deadly explosion at Ariana Grande concert People gather outside the arena. "We can confirm there was an incident as people were leaving the Ariana Grande show last night," police said on Twitter early on Tuesday. "The incident took place outside the venue in a public space. Our thoughts and prayers go out to the victims." Hide Caption 13 of 22

Photos: Deadly explosion at Ariana Grande concert People receive medical attention at a railway station close to the arena. The incident happened shortly after Grande had left the stage, shortly after 10:30 p.m. (5:30 p.m. ET) according to eyewitnesses. Calvin Welsford, an 18-year-old concertgoer, said that he heard a "loud bang" a couple of minutes after Grande's set had finished. Hide Caption 14 of 22

Photos: Deadly explosion at Ariana Grande concert Paramedics respond to the scene. Hide Caption 15 of 22

Photos: Deadly explosion at Ariana Grande concert Emergency workers and concert attendees gather outside the arena. Hide Caption 16 of 22

Photos: Deadly explosion at Ariana Grande concert People stand by a cordoned-off street close to the arena. Hide Caption 17 of 22

Photos: Deadly explosion at Ariana Grande concert Greater Manchester Police tweeted that emergency services were "responding to (a) serious incident at Manchester Arena. Avoid the area. More details will follow as soon as available." Hide Caption 18 of 22

Photos: Deadly explosion at Ariana Grande concert People are escorted away from the arena. Hide Caption 19 of 22

Photos: Deadly explosion at Ariana Grande concert People sit outside near the arena. The crowd was made up of mainly younger people who had come to see Grande in her first of three scheduled concerts in the UK. Hide Caption 20 of 22

Photos: Deadly explosion at Ariana Grande concert An injured man is helped at the scene. Hide Caption 21 of 22