In a possible terrorist attack Wednesday afternoon, a vehicle rammed into a crowd of pedestrians outside the British Parliament in London. A man then exited the vehicle and stabbed a police officer to death; other officers then shot and killed the assailant.

"Four people have died," said Britain's top counter-terrorism officer, Mark Rowley. "That includes the police officer who was protecting Parliament and one man we believe to be the attacker, who was shot by a police firearms officer."

The attack, which police are treating as terrorism, comes exactly one year after the series of suicide bombings in Brussels that killed 32, along with three bombers.

This post will be updated as further information becomes available.