Westminster attack: IS claim attacker as their 'soldier'
The person who carried out the "attack in front of the British parliament in London was a soldier of the Islamic State", an IS spokesman said in a statement via the militant-run Amaq news agency on Thursday.
The attacker "carried out the operation in response to calls for targeting citizens of the coalition", the statement added.
The group indicated no direct involvement in the incident, which British police believe was a lone attack "inspired by international terrorism".
British Prime Minister Theresa May told parliament on Thursday the attacker was born in Britain and had been investigated for links to religious extremism.
At least eight people were arrested in raids, some in the central city of Birmingham.
Islamic State group regularly claims responsibility for terror attacks despite having no direct involvement in the planning or facilitation.