The White House says the president praised the response of security forces and first responders and pledged “the full cooperation and support” of the U.S. government “in responding to the attack and bringing those responsible to justice.”

The White House says the two spoke by phone after a vehicle mowed down pedestrians on London’s Westminster Bridge. Around the same time, a knife-wielding attacker stabbed a police officer and was shot on the grounds outside Britain’s Parliament. The compound is in lockdown.

The head of counterterrorism at London’s Metropolitan Police has said that four people have died in what has been labeled a terror incident, including an attacker and a police officer.