The EU's counter-terrorism chief, Gilles de Kerchove, earlier this year said that IS foreign fighters did not represent the biggest threat.
One fan at the concert described how the explosion hit the venue as fans were leaving the building..
He said: "This has been the most horrific incident we have had to face in Greater Manchester and one that we all hoped we would never see". Our thoughts are now with our British friends. "Our thoughts and prayers go out to all those affected".
French President Emmanuel Macron said he was "horrified" by the attack.
Prime Minister Theresa May said in a statement: "We are working to establish the full details of what is being treated by the police as an appalling terrorist attack".
Paris Mayor Anne Hidalgo also expressed solidarity.
"Georgina was a lovely young student who was very popular with her peers and the staff and always made the most of the opportunities she had at the school", Peter Rawlinson, deputy of the Bishop Rawstorne Church of England Academy, said.
Campaigning ahead of next month's General Election in the United Kingdom has been suspended in the wake of a deadly suspected terror attack at a concert in Manchester.
GMP has said 22 people are known to have died and 59 injured. He provided no information about the individual who detonated the device. At least 22 people died in a suspected suicide bombing at a pop concert in the British city of Manchester this morning.
More than 400 officers were involved in the operation overnight. Among the victims were children.
Greater Manchester Police Chief Constable Ian Hopkins says police are treating the blast as an act of terrorism "until we know otherwise".
Grande herself appears to be uninjured.
"It makes me so angry and it breaks my heart that such a young and promising life has been stolen away!" "I don't have words".
The move to suspend campaigning follows the form established after the murder of Labour MP Jo Cox during the independence referendum campaign in 2016 when all major parties announced they would cancel events out of respect.
Artist BIA, who also performed, said in a tweet that she is OK.More news: Frontier Communications Corporation's (FTR), Rambus Inc.'s (RMBS)
More news: Trump arrives in Israel
More news: Manto poster is out at 70th Cannes Film Festiva!! Nawazzuddin looks intense
Both of their families have appealed for help in finding the girls safe and well.
Ulster Unionist leader Robin Swann said the attackers would not succeed.
In Tokyo, a spokesman for the Japanese government condemned the attack.
A large cordon remains in place around the arena and nearby Manchester Victoria Station, which was evacuated during the incident and remains closed, while forensic investigators gather evidence.
No, none of the identities of the people who were killed or wounded have been released.
Hotels opened their doors to people who could not get home due to an area lockdown.
"There were 60 ambulances last night, the injured are being treated at eight different hospitals across the Manchester region". The blast killed 19 people and injured dozens more.
In 2015, Pakistani student Abid Naseer was convicted in a U.S. court of conspiring with al Qaeda to blow up the Arndale shopping centre in the centre of Manchester in April 2009.
Twitter user JB said he was "not surprised" at what happened, accusing security of being "horrendous".
The department says the US public may experience increased security in and around public places and events.
Grande tweeted after news broke of the explosion saying she was "broken".
The government is urging US citizens in Manchester to heed directions from local authorities and be vigilant about their security. The explosion sparked panic as thousands of people rushed for the exits, witnesses told Reuters.
The incident sparked a nightlong search for loved ones as frantic parents tried to locate their teenage children, and groups of friends scattered by the explosion sought to find one another.
The 23-year-old Grande, true to her youthful fan base, is a social media phenomenon with 105 million followers on Instagram and 45.6 million followers on Twitter.
Fellow stars offered condolences as well. "My thoughts are with all those affected and our brilliant emergency services". "I'm sending all my love".