A full counter-terrorism investigation is under way after London attack, British police said Wednesday.Commander B.J. Harrington said "a number" of people have been injured, including police officers.

He said additional police officers, armed and unarmed, will be deployed across London during the evening rush hour as part of efforts to keep people safe.

A woman was killed, some 'catastrophic' injuries were reported after London terror attack in city's Westminster district on Wednesday in what appears to be a terrorist attack involving at least two linked events in which an attacker stabbed a police officer and another person ploughed a car into nearby pedestrians.

The threat level for international terrorism in the UK was listed at severe. Wednesday was the anniversary of suicide bombings in the Brussels airport and subway that killed 32 people.