"The attack started when a car was driven over Westminster Bridge, hitting an injuring a number of members of the public, also including three police officers on their way back from a commendation ceremony. The car then crashed near to parliament, and at least one man, armed with a knife, continued the attack and tried to enter parliament," Britain's top counter-terrorism officer Mark Rowley said.
"Sadly I can confirm that now four people have died. That includes the police officer who was protecting parliament and one man we believe to be the attacker who was shot," Rowley told reporters, adding that at least 20 people were injured.
London Metropolitan police said earlier in the day they were treating the events as terrorist incidents. The attack is currently being investigated.
A Sputnik correspondent reported from the scene.