British counterterrorism investigators searched two homes today and detained a number of people in the probe into a van and knife attack in the heart of London that left seven people dead.

Dozens were injured, many of them critically, in the attack that started on the London Bridge, when three attackers swerved the vehicle into pedestrians then, armed with knives, rampaged through Borough Market, slashing and stabbing anyone they could find.

The three men, who wore fake suicide vests, were shot to death by police.

The Islamic State group has claimed responsibility.

London's police chief says the attackers have been identified, but the names haven't been released.

At least 12 people were arrested yesterday, including five men and seven women ranging in age from 19 to 60.

One has since been released without being charged.