PARIS  - French President Nicolas Sarkozy on Tuesday vehemently denied new accusations of illegal party financing that are threatening to overshadow his re-election campaign.

An investigation into alleged illegal financing of Sarkozy's 2007 campaign by L'Oreal heiress Liliane Bettencourt is gathering momentum alongside campaigning for the two-round presidential election in April and May.

But the right-winger on Tuesday again denied any wrong-doing, saying that in 2007 his campaign funding "was contested by no-one".

"The campaign funding commission certified the accounts and said 'there isn't a centime whose origin is in doubt, there isn't an expense for which one doesn't know where payment comes from,'" he told Canal+ television.

Sarkozy said he was not surprised by the resurgence of the illegal funding claims, adding that in the run-up to an election a few "stink bombs" were always thrown.

This drew outrage from Socialist candidate Francois Hollande's camp. "To say that these are stink bombs is an insult to the justice system," said Jean-Marc Ayrault, a top Hollande advisor and leader of the Socialist parliamentary group.

Green candidate and former prosecutor Eva Joly last week called for Sarkozy to "give up his immunity (as head of state) and go and explain himself".

Investigating magistrate Jean-Michel Gentil has cited two dubious withdrawals of 400,000 euros each from Swiss bank accounts by an intermediary to Bettencourt's close aide Patrice de Maistre.

On March 23 Gentil, charged de Maistre with several alleged crimes and ordered him detained.

The first withdrawal was made on February 5, 2007, two days before a meeting between de Maistre and Eric Woerth, who was at the time treasurer of Sarkozy's first successful campaign.

Woerth later became labour minister but resigned in 2010 as the campaign financing probe gathered pace. In 2011 police carried out searches of his home and of the ruling UMP party's office in connection with the case.

Bettencourt's accountant, Claire Thibout, has testified to having been asked a number of times in 2007 to provide batches of 150,000 euros to Woerth.

The second questionable withdrawal was made on April 26, 2007 - four days after the first round of the presidential election and over a week ahead of the second round on May 6 that Sarkozy went on to win.

On April 26, former Bettencourt confidante and photographer Francois-Marie Banier wrote in his diary that the heiress told him: "De Maistre told me that Sarkozy had asked for money again. I said yes."

But Le Monde newspaper later quoted Banier as seeking to play down the significance of his diary entry when he was interviewed by judge Gentil.