The suicide bomber who killed 22 people outside an Ariana Grande concert in the U.K. had recently returned from Libya, it was reported on Tuesday.

Intelligence agencies are trying to determine whether Salman Abedi, who detonated a bomb just outside the Manchester Arena Monday night, received terror training in Libya, according to The Times of London.

The revelations came as thousands of troops were deployed to high-risk areas in the U.K. as the terror threat remained high.

A total of 22 people were killed in Monday night’s attack.