Abedi's 23-year-old brother has also been arrested.

Abedi killed 22 and injured 64 when he blew himself up outside an Ariana Grande concert on Monday night. An off-duty policewoman is among the dead, the BBC understands. 

The UK terror threat level is now up to its highest level of "critical".

This means more attacks may be imminent.

Military personnel are being deployed to protect key sites.

The Palace of Westminster has been closed to the public following police advice, and will not re-open until further notice, its website said.

Home Secretary Amber Rudd said: "[Monday's attack] was more sophisticated than some of the attacks we've seen before, and it seems likely - possible - that he wasn't doing this on his own."

Read MORE.

BBC News