Here’s what to know about the London Parliament attack

Updated at 11:22 a.m.

Four people, including a police officer and one man believed to be the attacker, died in an attack that London police are calling a “terrorist incident.” The suspect mowed down pedestrians in a vehicle on Westminster Bridge before fatally stabbing the officer outside the Houses of Parliament and being shot and killed, officials said.

Police said at least 20 people were injured in the attack.

“There has been a serious incident near to Parliament Square this afternoon which is being treated as a terrorist attack until the police know otherwise,” London Mayor Sadiq Khan said in a statement on Twitter.

While details are still emerging about the attack outside Parliament as well as another incident on Westminster Bridge, here are the key details to know:

An Attack Took Place Outside The British Parliament

A police officer was stabbed outside the Houses of Parliament in the British capital, the Associated Press reports.

The “alleged assailant was shot by armed police” said the leader of one of the Houses of Parliament, David Lidington, the New York Times reports. British lawmakers reported having heard multiple gunshots close to Parliament.

A Downing Street source has told the BBC that the Prime Minister, Theresa May, is safe. “The Prime Minister was brought back to Number 10 from Parliament,” her spokesperson told the BBC. She is currently monitoring the situation.”

There Are Also Reports of an Attack Near Westminster Bridge

A vehicle on the nearby Westminster Bridge ran down pedestrians, the AP reports. Mary Creagh, a Labour Party lawmaker, said she believed between five and six people were run down on the bridge, according to the AP.

How Many People Were Injured

Scottish Yard commander B.J. Harrington said in a press conference on Wednesday that he could not confirm numbers but that there were a “number of casualties, including police officers.”

The Area Has Been Placed on Lockdown

British MPs in Parliament have been instructed to remain inside the chamber. Other MPs have been evacuated. Political journalists were also told to remain inside the building.

The surrounding area, including Parliament Square, as well as the nearby tube station of Westminster, were closed, the BBC reports. The London Eye, a key landmark, has also been placed on lockdown, according to the outlet.

What World Leaders Have Said

President Donald Trump said at a brief press appearance on Wednesday that the event was “big news,” the AP reports. Trump’s spokesman, Sean Spicer, says the U.S. will continue to monitor the situation and update the President, according to the AP.

The U.S. State Department spokesman Mark Toner said in a statement: “We stand ready to assist in any way the U.K. authorities would find helpful.”

This article originally appeared in TIME.