ISIS supporters have been celebrating on social media after a terrorist attack on Tuesday targeted a concert venue in the north of England, killing at least 19 people and injuring more than 50.

Twitter accounts belonging to ISIS have used hashtags referring to the incident in order to post their celebratory messages. Some users also encouraged similar attacks on other regions.

The attack was described by ISIS supporters as an act of revenge in response to air strikes in Iraq and Syria.

“It seems that bombs of the British airforce over children of Mosul and Raqqa has just came back to #Manchester,” a user said on Twitter, referring to the British government’s airstrikes on Iraqi and Syrian cities.

Another user said he hoped ISIS was responsible for the attack. “We hope that the perpetrator is one of the soldiers of the caliphate.”

ISIS has not yet claimed responsibility.

British police have said that they recognize the blast at the Manchester Arena as a “terrorist incident”.

If confirmed, this would be deadliest terrorist attack on Britain since July 2005 when 52 people were killed in suicide bombings on London’s transport system.

Two unnamed officials said that initial signs pointed to a suicide bomber as being responsible for the attack.