Prosecutors investigated claims yesterday that President Nicolas Sarkozy's campaign got illegal cash from France's richest woman, as the scandal spawned lawsuits and a fierce fightback by his allies.

The prosecutor's office in the Paris suburb of Nanterre asked the fraud squad to probe allegations made by a former accountant for Liliane Bettencourt, heiress of the L'Oreal cosmetics empire.

Mr Sarkozy's allies hit back, accusing the media of "fascist" tactics and dismissing as a smear campaign the scandal which has plunged him into the biggest crisis of his presidency. Labour Minister Eric Woerth has decided to make an official complaint over the allegations, counter-alleging that he was the victim of "malicious falsehood" by persons unknown, his office said yesterday.

"He denounces the false accusations to which he has been subjected," the Labour Ministry said in a statement.

A French magistrate will study his complaint and decide whether criminal charges can be brought.

Prime Minister François Fillon rebuffed mounting calls for a ministerial reshuffle to clear the air, vowing: "We will not give in to this upheaval."

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