LONDON, May 23./TASS/. British Prime Minister Theresa May called the blast at Manchester Arena late on Monday an "appalling terrorist attack".

"We are working to establish the full details of what is being treated by the police as an appalling terrorist attack," she said in a statement.

"All our thoughts are with the victims and the families of those who have been affected," the prime minister said.

Earlier, police said at least 19 people were killed and about 50 were injured in a blast at Manchester Arena after a concert of American pop singer Ariana Grande.

The blast "is currently being treated as a terrorist incident until police know otherwise," Greater Manchester Police tweeted. According to eyewitnesses, there were mostly teenagers among the concertgoers.