A French magazine is claiming that President Nicolas Sarkozy and Libya's ex-strongman Moamer Kadhafi reached a "secret deal" to trade nuclear cooperation for the release of foreign medics.

Based on "confidential documents", the report to appear Wednesday in weekly Les Inrockuptibles emerged ahead of Sunday's run-off vote between Sarkozy and Socialist frontrunner Francois Hollande.

It came after Sarkozy, who has accused "biased" left-wing media of targeting him, said he would sue a website that claimed Kadhafi financed his 2007 campaign.

Neither the foreign ministry nor the presidency would comment on the report in Les Inrockuptibles, which the magazine said was based on diplomatic cables issued in the week before the medics' release.

The five Bulgarian nurses and a Palestinian doctor, jailed eight years on charges of infecting children with the AIDS virus, were released on July 24, 2007 following French intervention.

Sarkozy travelled to Tripoli the day after their release, overseeing the signature of arms contracts and a nuclear cooperation accord and inviting Kadhafi to Paris later that year.

The magazine quoted a diplomatic cable received by France's then envoy to Tripoli, Jean-Luc Sibiude, on July 16 as saying he should "approach Libyan authorities at the highest level to submit a draft framework agreement on Franco-Libyan cooperation".

In a return cable two days later the envoy told Paris that Tripoli was particularly interested in "nuclear" cooperation, saying: "The Libyans were waiting for this signal, which meets a personal demand of Colonel Kadhafi," the magazine reported.

On the night of July 23, the ambassador received a new cable announcing that Paris had accepted a nuclear deal but noting that France would agree "only if the nurses and doctor are freed", the magazine said.

They were released the next day.

Speaking before a parliamentary commission in 2007, Sarkozy's then chief of staff Claude Gueant, now the interior minister, said there had been no "trade-offs" in ensuring the medics' release.