ISIS supporters celebrate Manchester attack online, no official claim

British Prime Minister Theresa May said the blast was being treated as a terrorist attack

Islamic State supporters celebrated on social media on Tuesday after a blast at a concert venue in the north of England killed at least 19 people, although the militant Islamist group has not formally claimed responsibility.

British police have said they are treating the blast at the Manchester Arena at the end of a concert by US singer Ariana Grande as a "terrorist incident". More than 50 people were wounded.

Twitter accounts affiliated to Islamic State have used hashtags referring to the blast to post celebratory messages, with some users encouraging similar attacks elsewhere.

Some messages described the attack as an act of