Islamic State was responsible for an attack outside Britain's parliament which left four people dead, the group's Amaq news agency said on Thursday.

"The perpetrator of the attacks yesterday in front of the British parliament in London is an Islamic State soldier and he carried out the operation in response to calls to target citizens of the coalition," the Amaq statement said.

Islamic State, which has controlled parts of Iraq and Syria in recent years, has lost territory this year to local forces in those countries supported by a U.S.-led military coalition.