Four people were killed and at least 20 others were injured in an attack outside the British Parliament on Wednesday. Here's what you need to know.

• Around 3 p.m. on Wednesday, a suspect drove a vehicle into pedestrians along the Westminster Bridge in London. The suspect crashed into a railing before fleeing the vehicle.

• After fatally stabbing one police officer, the suspect was shot and killed by another officer, The New York Times reported.
• The attack took place on the one-year anniversary of a suicide bombing in Brussels that left 32 people dead.

• Officials haven't identified the suspect or attributed a motive to the attack yet, but the London Metropolitan Police announced that a "full counterterrorism investigation is underway" during a press conference Wednesday.
• The Metropolitan Police has officially declared the attack a "terrorist incident," The Guardian reported.

• The British Prime Minister was evacuated and the Parliament building was placed on lockdown in response to the attack.
• Law enforcement said that there was only one suspect involved in the attack, according to the Associated Press.

This story is developing, and ATTN: will update with more information as it becomes available.