Damaging new claims have emerged about the funding of Nicolas Sarkozy's 2007 election campaign and his links with former Libyan leader Muammar Gaddafi emerged.

The French investigative website Mediapart claims to have seen a confidential note suggesting Gaddafi contributed up to €50m (£42m) to Sarkozy's election fund five years ago.

Similar allegations emerged a year ago when Gaddafi's son Saif al-Islam claimed Libya helped finance the 2007 campaign and demanded the French president, who led the war on the Libyan leader, return the money.

In an interview with the Euronews TV channel, Saif al-Islam, who is currently being held in Libya after his father's defeat and death, threatened to make details of the bank transfers public after the French leader threw his weight behind opposition forces.

The latest allegations come at a crucial time for Sarkozy who is seeking a second term in office in a two-round election in under six weeks.

Mediapart journalist Fabrice Arfi told the Guardian he had seen leaked documents contained in the legal dossier of the affair, currently under investigation by a judge.

"We knew these documents existed but it is the first time we have had the details of what was in them," he said.

"And there are lots of details, including dates, places and amounts."

One document, a government briefing note, allegedly points to visits to Libya by Sarkozy and his close colleagues and advisers, which it says were aimed at securing campaign funding.

Shortly after Sarkozy's election, Colonel Gaddafi was invited to Paris and allowed to pitch his bedouin tent in the grounds of an official French residence close to the Elysée Palace. He was described as the "Brother Leader" by the French.

When previously asked about Saif al-Islam's claims, a spokesman for the Elysée Palace told Le Monde: "We deny it, quite evidently."