The death toll from the Westminster terror attack has risen to five, police have said.

That includes three members of the public, the attacker, who was shot dead, and a police officer, Metropolitan Police Acting Deputy Commissioner Mark Rowley has told a press conference.

Mr Rowley named the slain officer as 48-year-old PC Keith Palmer, a member of the Parliamentary and diplomatic protection command. He was married and a father, and had served as a police officer for 15 years, Mr Rowley said.

In total about 40 people have been injured, including three police officers of whom two are in serious condition, he added.

He declined to name the attacker but said he was believed to have been inspired by international terrorism. "We think we know who the attacker is," he said. "Islamist-related terrorism is our assumption."

The carnage unfolded at about 2.40pm after the attacker drove through pedestrians on Westminster Bridge, before crashing into railings and trying to enter Parliament.

Prime Minister Theresa May has condemned the killings as "sick and depraved".

She also praised praised police and emergency responders who ran towards the danger "even as they encouraged others to move the other way".

London Mayor Sadiq Khan has pledged Londoners "will never be cowed by terrorism" and said: "London is the greatest city in the world, and we stand together in the face of those who seek to harm us and our way of life.

"We always have and we always will."

Mr Rowley said: "Terrorists have a clear aim. That is to create discord, distrust and to create fear. The police stand with all communities in the UK and will take action against anybody who seeks to undermine society, especially where their crimes are motivated by hate.

"Our investigation continues and is moving at a very fast pace. We have hundreds of officers on this investigation and they are focusing on the suspect's motivation, preparation and his associates.