Cincinnati: Republican John McCain quickly denounced the comments of a conservative radio talk show host who while warming up a campaign crowd referred repeatedly to Barack Hussain Obama and suggested the Democrat was an unsavoury politician.

Hussain is Obama's middle name, but talk show host Bill Cunningham used it three times as he addressed the crowd on Tuesday before the likely Republican nominee's appearance.

False rumours about Obama having Islamic ties are circulating on the Internet and some opponents have used his middle name to try to link him with former Iraqi leader Saddam Hussain.

"Now we have a hack, Chicago-style Daley politician who is picturing himself as change. When he gets done with you, all you're going to have in your pocket is change," Cunningham said as the audience roared.

Chicago is known for its legendary political machine that historically doled out jobs and favours in exchange for support for Democrats on Election Day. The courts have mostly dismantled the machine by outlawing political patronage, but the city's powerful Democrats - like Mayor Richard Daley - can still turn out the vote.

'I take responsibility'

McCain was not on stage nor in the building when Cunningham made the comments, but he quickly distanced himself from them and the talk show host after finishing his speech. McCain spoke to a couple hundred people at Memorial Hall in downtown Cincinnati.

"I apologise for it," McCain told reporters, addressing the issue before they had a chance to ask the Arizona senator about Cunningham's comments.

"I did not know about these remarks but I take responsibility for them. I repudiate them," he said.