Right-wing incumbent Sarkozy is slowly clawing back points from Socialist frontrunner Francois Hollande, whose own presidential bid has been hit by the intrusion of disgraced IMF chief Dominique Strauss-Kahn into the campaign.
Both candidates have been appealing to the 18 percent of voters who chose anti-immigrant candidate Marine Le Pen in the April 22nd first round, with Sarkozy riding on the back of rhetoric inspired by her National Front party.
Sarkozy on Monday dismissed as a "crude forgery" a document published by left-wing investigative website Mediapart alleging the former Libyan dictator agreed to give €50 million ($66 million) to Sarkozy's campaign in 2007.
"We will file a suit against Mediapart... this document is a crude forgery, the two people supposed to have sent and received this document have dismissed it," Sarkozy told France 2 television.
Sarkozy and his supporters believe that he is relentlessly targeted by "biased" left-wing media, while the incumbent has repeatedly sought to portray himself as a victim now repenting his perceived "bling bling" style.
"There's a section of the press, of the media, and notably the site in question whose name I refuse to mention, that is prepared to fake documents. Shame on those who have exploited them," Sarkozy said.
Claims that Qaddhafi financed Sarkozy's 2007 campaign are not new, but Mediapart's document bearing the signature of Libya's former foreign intelligence chief Moussa Koussa is.
The letter was addressed to Bashir Saleh, Qaddhafi's former chief of staff and head of Libya's $40-billion sovereign wealth fund, who is currently resident in France.
But Saleh's lawyer said he had "grave reservations" about the document while Koussa, who now lives in Qatar, said: "All these allegations are false."
Hollande said that it was up to judges to decide on the veracity of the Libyan allegations.
"If it's a fake then the site will be found guilty, if it's not a fake then he (Sarkozy) will have some explaining to do," Hollande said, denying any link to Mediapart which Sarkozy has branded "an agency in the service of the left."
Hollande's team meanwhile sought to play down the re-emergence of one-time presidential hopeful Strauss-Kahn into the race, after the man known in France as DSK attended a Socialist lawmaker's birthday party in Paris.
MP Julien Dray on Saturday invited senior members of his party to his birthday drinks party at a popular disco bar on the notorious Rue St Denis, a street which has historically been associated with prostitution.
But Dray did not warn his guests he had invited Strauss-Kahn, who became a toxic figure last year when he was accused of sexual assault in New York and is now under investigation in France over alleged ties to a vice ring.
"He no longer has a role in political life and thus should not be part of a campaign nor in any images that could potentially lead people to believe he's coming back," Hollande said on Sunday.
Hollande's former partner Segolene Royal, who was beaten by Sarkozy in the 2007 presidential race, said that the former IMF chief's presence at the party was "inconsequential".
"I at first thought it was a joke. Then I thought that it was in very bad taste," she told BFM-TV, adding that "I left immediately."
"I don't want to meet DSK, given what happened which damaged the dignity of women," Royal said.
An Ipsos poll published on Monday said that Hollande would win Sunday's run-off 53 percent to 47 percent, after the Socialist dropped a percentage point to Sarkozy compared to the last poll on April 22nd.
Nevertheless, 22 percent of those questioned said they would go and vote but declined to say for whom.
The Ipsos poll said that 54 percent of far-right candidate Le Pen's voters would go for Sarkozy in the run-off, while 14 percent of them would vote for Hollande.
Both candidates have a number of major rallies planned for the final week of campaigning, and will face each other on Wednesday in a televised debate that could prove to be Sarkozy's last chance for a breakthrough.