Details were slowly emerging from what British police called a major terrorist incident outside the Palace of Westminster that has left at least one person dead and several with life-threatening injuries in the center of London.

Four people have been confirmed dead in the incident and at least 20 have been injured.

Police said a man armed with a knife was shot after he attacked a law enforcement officer outside Britain's Houses of Parliament. In what appears to be a related incident -- possibly involving the same attacker -- a driver was said to have deliberately ploughed into pedestrians on Westminster Bridge, which runs adjacent to the parliament, killing at least one and injuring dozens more.

Here is what we know as of 16:45 GMT, approximately two hours after the incident was first reported:

U.K. Parliament remains on lockdown and all sessions are suspended until further notice.

Lawmakers are being released from the Palace, which remains under heavy exterior security.

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Prime Minister Theresa May has returned to her official residence at Downing Street and is safe.

PM will chair a Cabinet Office Briefing Room, or COBRA meeting later Wednesday

COBRA meetings are called in response to civil emergencies 

Metropolitan Police have confirmed "a number" of casualties, including police officers

Additional officers are being deployed across the capital 

Scottish Parliament has suspended a debate on its referendum bill.

Tourists attractions around Westminster, including the London Eye, and public transport stations are closed.

London's Mayor, Sadiq Khan, has issued an official statement via his verified social media account