The prime minister has apologised for "any misunderstanding" after calling former imam Sulaiman Ghani a supporter of so-called Islamic State, Downing Street has said.
David Cameron made the comments about Mr Ghani in the House of Commons when he accused Sadiq Khan of sharing a platform with extremists "again and again and again" during the London mayoral race.
During Prime Minister's Questions, Mr Cameron told MPs: "I am concerned about Labour’s candidate as mayor of London who has appeared as again and again and again.
"The leader of the Labour party is saying it is disgraceful. Let me tell him, Sulaiman Ghani. The honorable member for Tooting has appeared on a platform with him nine times.
"This man supports IS [Islamic State]. I think they are shouting down this point because they don’t want to hear the truth."
Downing Street said Mr Cameron was referring to reports Mr Ghani supports "an" Islamic state.
A Number 10 spokesman said: "In reference to the Prime Minister's comments on Sulaiman Ghani, the Prime Minister was referring to reports that he supports an Islamic state.
"The Prime Minister is clear this does not mean Mr Ghani supports the organisation Daesh and he apologises to him for any misunderstanding."
Mr Ghani, a former imam at the Tooting Islamic Centre, has threatened legal action after being described as a supporter of the jihadist group.
Mr Khan beat Zac Goldsmith, the Conservative candidate, to become the new London mayor in elections last week.