Mark Rowley

Russian former double agent Sergei Skripal and his daughter Yulia remain in a critical condition in intensive care in hospital, British police said on Wednesday as they appealed for witnesses to come forward with any information about the case, Reuters reported.

Theresa May last night raised the terror threat level to critical as police scrambled to identify the attackers who tried to blow up a packed Tube train during the morning rush hour, in the fourth assault to strike London this year. At least 29 people were injured in the blast and stampede, including victims requiring hospital treatment for severe burns.

A home-made bomb exploded on a packed rush-hour commuter train in London injuring 22 people on Friday, police said, in what was being treated as the fifth terrorism attack in Britain this year.

Passengers on board a train heading into the capital fled as fire engulfed a carriage at Parsons Green underground station in West London after the explosion at 8.20 a.m. (0720 GMT).

A homemade bomb on a packed rush-hour commuter train in London engulfed a carriage in flames and injured 22 people on Sept. 15 in what police said was Britain's fifth terrorism incident this year, but apparently failed to fully explode.

Three men wearing fake suicide bomb vests struck at the heart of the capital after driving a van into pedestrians on London Bridge before stabbing bystanders in a bloody rampage.

In an attack lasting little over eight minutes, the gang allegedly screamed “this is for Allah” before killing seven and injuring up to 48 people.

All three were shot dead by armed cops.

Six people have been killed and at least 48 injured in a terror incident in London in which three male attackers were shot dead by police, BBC reported.

A white van hit pedestrians on London Bridge at about 22:00 BST on Saturday, then three men got out and stabbed people in nearby Borough Market.

Police said the three men were wearing fake bomb vests.

Seven people were killed, three attackers are dead and 48 victims have been transported to hospitals after a “terrorist incident” in London Saturday night involving a vehicle reportedly plowing into pedestrians on London Bridge and reported stabbings at Borough Market, officials said.

Seven people were killed in a terror attack on June 3 by three assailants on London Bridge and in the bustling Borough Market nightlife district, the chief of London's police force said on June 4.

"It has now been confirmed sadly that seven members of the public have died," Cressida Dick told reporters, raising the toll from six victims earlier.

British police said March 24 they had made two further "significant" arrests over the Islamist-inspired terror attack on parliament, as they appealed for information about the homegrown killer, born Adrian Russell Ajao, who left four people dead.

Two more people have been arrested over Wednesday's terror attack in London, police said on Friday, also giving the attacker's birth name as Adrian Russell and appealing to the public for information about him, AFP reports.