The claim, made in the conservative Insight magazine, also revealed the Machiavellian scheming of political activists in a presidential race still nearly two years away.

It was aimed at tarnishing Mr Obama’s image in the week he announced himself as a White House contender. But the article also claimed that the madrassa allegations came from aides to Hillary Clinton, Mr Obama’s main opponent for the Democratic nomination.

This may be wishful thinking on behalf of Republicans. The Clinton camp is determined not to be accused of digging dirt on Mr Obama because they fear such tactics could backfire, given his popularity.

But the Insight allegations represent an exquisite double shot at the Democrats’ two leading White House contenders: it implies that Mr Obama, whose middle name is Hussein, is a closet Islamic extremist, and that Mrs Clinton is so rattled by his candidacy she is using underhand tactics to weaken him.

Mr Obama, who is expected to announce formally his candidacy on February 10, has never been subjected to the hardball tactics of the presidential arena — until yesterday. Last night an aide said that the campaign was working on a formal statement, but added that the claims were “not accurate”.

The online article begins: “Are the American people ready for an elected president who was educated in a madrassa as a young boy and has not been forthcoming about his Muslim heritage?” It continues: “This is the question Senator Hillary Rodham Clinton’s camp is asking about Senator Barack Obama.”

Mr Obama’s mother was a white woman from Kansas; his father, a black Kenyan Muslim. He states in his recent biography that he attended a predominately Muslim school when he lived in Jakarta as a teenager.

But the article claims: “In Indonesia, the young Obama was enrolled in a madrassa and was raised and educated as a Muslim.” It says that Mr Obama omitted to say in his memoir, or at any other time, that he attended the school for four years.

Mr Obama, who has spent his adult life in Chicago, calls himself a Christian and says that he believes in God. He attends a local church.

A source close to the Clinton campaign told The Times, a day before the Insight article was published, that they do not want to be seen as attacking Mr Obama or digging for dirt, but that they would be happy for another Democrat contender to criticise him.

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