A British Muslim group on Friday condemned an alleged smear campaign against Sadiq Khan, who has become London's first Muslim mayor.Shuja Shafi, the head of the Muslim Council of Britain, congratulated Khan on his apparent victory but said it was "unfortunate that a Londoner who happens to be Muslim, and has gone out of his way to repudiate extremists, has nevertheless been smeared with the extremist brush."The Muslim Council of Britain, which aims to represent an estimated 2.7 million British Muslims, was referring to the campaign by Khan's Conservative rival, Zac Goldsmith, who was strongly backed by Prime Minister David Cameron.Goldsmith labelled Khan a "radical," published apparently untrue statements about him in campaign leaflets aimed at voters of South Asian origin, and accused him of associating with extremists.In parliament later, Cameron claimed Khan had "appeared on a platform with Suliman Gani nine times; this man [Gani] supports [Daesh]."Shafi said Gani, a Muslim cleric, had been unable to challenge the claims, since British libel laws do not apply to statements in parliament.Shafi called the claims part of a "smear-by-association" attempt that "has become all too common for Muslims and Muslim organisations."Gani defended himself by saying he had "campaigned against the evils of Daesh," while Khan said Cameron's intervention showed Goldsmith was "continuing his divisive, Donald Trump-style campaign."Khan said he had attended the same events as Gani and other outspoken Muslims, but only in his capacity as a human rights lawyer."We urge the Conservative Party to reflect and learn from this disreputable period of campaigning so that we can all draw a line and move on," Shafi said on Friday.