London attacker identified as Khalid Masood

The man believed to have been responsible for the terrorist attack in Westminster has been identified as 52-year-old Khalid Masood.

The Metropolitan Police say Masood was born in Kent, but is thought to have been living in the West Midlands recently, adding that Masood was also known by a number of aliases, the CNN reported.

"Masood was not the subject of any current investigations and there was no prior intelligence about his intent to mount a terrorist attack," the police said in a statement.

Earlier in the day, the Islamic State claimed responsibility for the Westminster attack that claimed the lives of four and injured 40 others.

British Prime Minister Theresa May has said the attacker behind the terrorist rampage at the gates of the Houses of Parliament was a British-born man previously known to MI5 due to concerns over violent extremism.

"The assailant, who was shot dead on Wednesday as he attacked police officers in the shadow of Big Ben, was considered to be a peripheral figure and had fallen from the intelligence picture," May told a packed House of Commons.

"Attacker was British born and thought to be inspired by Islamist ideology," May said.

As many as four people died after a terrorist attacked Westminster, stabbing a police officer to death as he tried to storm the Parliament, and killing three members of the public as he careered through the heart of the capital in a 4x4 vehicle, according to the Guardian.