London authorities believe Islamist-related terrorism is behind the Westminster attack. The police said they think they already know who the attacker is as the death toll for the attack has risen to five already.
The death casualties include three members of the public, the attacker who was shot dead and a police officer.
40 people have been injured, including three police officers. Two of the officers are in serious condition.
Prime Minister Theresa May said the attack on the heart of the capital was " sick and depraved". She said the attack was an attempt to defeat UK values but said they will not succeed.
May also said that the location of the attack was no accident. She said the terrorist chose to strike at the heart of the capital city where people of all nationalities, religions, and cultures come together to celebrate the values of liberty, democracy, and freedom of speech.
A car drove into people on Westminster Bridge before reaching the House of Parliament. After the vehicle crashed into the railings of the Houses of Parliament, a man with a knife continued the attack. The attacker tried to enter the building. The suspect attacked an unarmed police officer with a knife, attempted to attack another police officer before he was shot and killed by other police authorities.
The police officer killed by the attacker has been identified as 48-year old Keith Palmer.
The Parliament was put on lockdown after the attacks, but the lockdown has since been lifted this evening. London police are also working at reducing areas that have been cordoned off from the public following the attacks.
UK threat level has been categorized as "severe" even before the attacks and will remain at that level.
London Mayor Sadiq Khan said his city will not bow down to terrorism. He called London the " greatest city in the world" and that the people will be united in the face of threats to harm them and their way of life.
Police authorities reminded the public that terrorists have a clear aim, and that is to create discord, distrust, and fear among the people.