London (PTI): At least three people were killed and 20 injured as terror struck the British capital when a man mowed down pedestrians on a bridge and stabbed a police officer outside parliament complex before being shot dead by Scotland Yard officers.

The head of counterterrorism at London’s Metropolitan Police, Mark Rowley said the dead policeman was among the armed officers who guard Parliament while the other victims died on Westminster Bridge after the attacker mowed down pedestrians in a car, leaving at least 20 people injured.

At least three other police officers were also injured in the attack.

A search is underway to make certain no other attackers are in the area though police believe there was only one attacker.

“We are satisfied at this stage that it looks like there was only one attacker. But it would be foolish to be overconfident early on,” he said.

“We are carrying out a full investigation into the events. Our strength as a city is our ability to stand together. We will do all we can to protect the people of London,” he added.

Scotland Yard had earlier called on the public to remain vigilant and said a review of policing strategy across the city was underway, with additional police officers being deployed across London.

The Indian High Commission in London has set up a special Public Response Unit for any Indians caught up in today s terror attack.

The incident unfolded on Wednesday afternoon as a man tried to gain entry into the British Parliament via the main entrance and stabbed a police officer.

Plainclothes armed officers shouted warnings at him before shooting a number of rounds.

He was later seen being covered by blankets, presumed dead.

UK Foreign Office minister Tobias Ellwood administered mouth-to-mouth resuscitation to the stabbed police officer but said he died at the scene .

In an incident just minutes earlier, a speeding grey Hyundai i40 mowed down several pedestrians on Westminster Bridge nearby before ramming into the iron railings of the side of the House of Commons building.

The driver from this vehicle is believed to be the lone knife-man who then ran out of the vehicle to try and enter the Parliament building, where he attacked the police officer and was eventually shot dead.