Islamic State was responsible for an attack outside Britain's parliament that left four people dead, the group's Amaq news agency said on Thursday.
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London Police have named the attacker as Khalid Mahsood.
"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.
Earlier on Thursday, British Prime Minister Theresa May told the House of Commons that the London attacker was British-born and earlier investigated by MI5 for links to violent extremism.
May says police believe the man acted alone and there is no reason to believe "imminent further attacks" are planned.
Police arrested seven people as part of an investigation into the lone-wolf attacker who killed three people and injured 40 before being shot dead by police near parliament in London on Wednesday, Britain's most senior counter-terrorism officer said.