ISIS Supporters Celebrate Ariana Grande Concert Explosion in Manchester

manchester attack
Armed police officers stand next to a police cordon outside the Manchester Arena, where U.S. singer Ariana Grande had been performing, in Manchester, England, on May 23. Andrew Yates/Reuters

Supporters of the Islamic State group (ISIS) are celebrating an explosion at an Ariana Grande concert in Manchester, England, that has killed at least 19 people and left another 50 injured. Social media accounts linked to ISIS supporters were posting messages supporting the deadly incident Monday night at the sold-out 21,000-capacity Manchester Arena.

The group has not claimed responsibility for the explosion, nor have any others, but police said they were investigating the incident as a terrorist attack.

Related: Ariana Grande concert live updates: Deaths confirmed in explosion in Manchester

One pro-ISIS post, highlighted by Rita Katz, a co-founder of the private intelligence firm Search International Terrorist Entities Intelligence Group, said, "Kill him everywhere, Britain and England and Manchester and UK and Britain." Other accounts were linking to the first statement about the attacks by Greater Manchester Police.

1) No claim regarding blast in #Manchester, but #ISIS accounts celebrating the attack, disseminating media & threats

— Rita Katz (@Rita_Katz) May 23, 2017

Pro-ISIS users called the incident a "successful and surprising blow" to Britain. It was framed as retaliation for the airstrikes that Britain has been carrying out on ISIS targets in Iraq and Syria.

2) Pro-#ISIS forum users call #Manchester attack “a successful and surprising blow,” to #Britain, frame attack as retaliation for airstrikes

— Rita Katz (@Rita_Katz) May 23, 2017

Michael Smith, a U.S.-based terrorism analyst, linked to further posts celebrating the attack on ISIS-linked Telegram channels. He said such response online was a "strong indicator" the attack was linked to the group.

BREAKING Key Islamic State-linked Telegram channel now touting initial official statement re ostensible terrorist attack in #Manchester

— Michael S. Smith II (@MichaelSSmithII) May 23, 2017

SCREENSHOTS Growing celebrations of situation in #Manchester on key Islamic State-linked Telegram channels. Strong indicator of IS linkage

— Michael S. Smith II (@MichaelSSmithII) May 23, 2017

There were similar posts from ISIS supporters online following an attack near British Parliament in London in March. (The group later claimed responsibility for that attack.)

The source of Monday's explosion was reportedly a nail bomb, the same type of device ISIS used in an attack in Brussels in March 2016.