At least 22 people were killed and 59 wounded when a suicide bomber struck as thousands of fans streamed out of a concert by US singer Ariana Grande in the English city of Manchester on Monday night.
Children were among the dead, police said. At least 12 children under the age of 16 were among the 59 injured, a UK ambulance official said.
One of the first victims to be identified was 18-year-old Georgina Callander, whose friends shared on social media a picture of her taken with Grande some months ago. The second victim identified is eight-year-old Saffie Rose Roussos.
Daesh claimed responsibility on Tuesday. US officials later identified the suspected suicide bomber as Salman Abedi,
Britain's Queen Elizabeth II condemned the attack: "The whole nation has been shocked by the death and injury in Manchester."
"I would like to express my admiration for the way the people of Manchester have responded, with humanity and compassion, to this act of barbarity," the Queen said.
TRT World's Simon McGregor-Wood brings more.
May addresses the nation
Prime Minister Theresa May said the incident was being treated as a terrorist attack, making it the deadliest such assault in the UK since four British extremists killed 52 people in suicide bombings on London's transport system in July 2005.
May said police and security services knew the identity of the Manchester bomber, but were not ready to release the name.
She also said the attacker had carried out the attack alone but it was not yet clear if others had helped in the preparation.
Police have made one arrest in connection with the attack.
"With regards to the ongoing investigation into last night's horrific attack at the Manchester Arena, we can confirm we have arrested a 23-year-old man in South Manchester," police said.
The blast occurred as the audience was leaving Grande's concert in the northern English city.
A witness who attended the concert said she felt a huge blast as she was leaving the Manchester Arena, followed by screaming and a rush by thousands of people trying to escape the building.
"We were making our way out and when we were right by the door there was a massive explosion and everybody was screaming," concert-goer Catherine Macfarlane said.
A dark night
broken.— Ariana Grande (@ArianaGrande) May 23, 2017
from the bottom of my heart, i am so so sorry. i don't have words.
Police said the attacker died after detonating explosives shortly after 10:33 pm (2133 GMT) at Manchester Arena, Europe's largest indoor concert venue, with the capacity to hold 21,000 people.
"We believe, at this stage, the attack last night was conducted by one man," Manchester Chief Constable Ian Hopkins told reporters. "The priority is to establish whether he was acting alone or as part of a network.
"The attacker... died at the arena. We believe the attacker was carrying an improvised explosive device which he detonated causing this atrocity."
Britain on alert
Prime Minister May called an emergency meeting with intelligence chiefs on Tuesday morning.
London Mayor Sadiq Khan said more police had been ordered onto the streets of the British capital following the assault.
A source with knowledge of the situation said the bomber's explosives were packed with metal and bolts. At least 19 of those wounded were in a critical condition, the source said.
The attack comes ahead of a general election in the United Kingdom in which security has been a campaign issue.
Prime Minister May said her thoughts were with the victims and their families. She and Jeremy Corbyn, the leader of the opposition Labour Party, agreed to suspend campaigning ahead of the June 8 election.
"We are working to establish the full details of what is being treated by the police as an appalling terrorist attack," May said in a statement. "All our thoughts are with the victims and the families of those who have been affected."
Terrible incident in Manchester. My thoughts are with all those affected and our brilliant emergency services.— Jeremy Corbyn (@jeremycorbyn) May 22, 2017
Reaction from world leaders
German Chancellor Angela Merkel voiced her "sorrow and horror" over Monday's attack.
French President Emmanuel Macron who plans to speak to May about terror strategy voiced his "horror" at the assault.
Macron "learnt with horror and shock about the attack that occurred yesterday evening," his office said in a statement.
French Prime Minister Edouard Philippe condemned the suicide attack as "the most cowardly terrorism" that was aimed "specifically and knowingly" at young people.
Turkey's President Recep Tayyip Erdogan strongly condemned the attack, saying Turkey stands by the UK and other countries in their fight against terrorism.
US President Donald Trump called those behind the attack "evil losers," and said the US stands in "absolute solidarity" with the British people.
Chinese President Xi Jinping sent his condolences over the blast to Britain's Queen Elizabeth, Chinese state media reported.