Some EU officials fear Sarkozy will take the limelight if the medics are released.
An EU delegation is in Tripoli negotiating with the Libyan government.
The delegation includes Benita Ferrero-Waldner, the EU’s external relations commissioner, Cecilia Sarkozy, the wife of Nicolas Sarkozy, the French president and Claude Gueant, a French presidential aide.
A spokewoman for Ferrero-Waldner stressed there was no certainty about a possible return date for the six.
She said: “We are hoping for a result as soon as possible but we have no idea” when it could happen.
Ivailo Kalfin, the Bulgarian foreign minister, also remained cautious about the chances that the health workers would soon be repatriated.
Kalfin said: “I expect the talks to be finalised today. We are now at the stage where the decision is purely political. If the Libyans show good will enough the transfer can be done very quickly.”
Nicolas Sarkozy, speaking in France, said of the talks: “What I know is that it’s very tough. This has been going on for eight-and-a-half years.”
He refused to confirm reports from the government in Tripoli that he would travel to Libya on Wednesday to meet Colonel Muammar Gaddafi, the Libyan leader, in a bid to try to drive the negotiations forward.
As part of the latest European effort to secure the health workers’ release, Cecilia Sarkozy met with Aicha Gaddafi, the 28-year-old daughter of the Libyan leader, who runs a charity.
Nicolas Sarkozy also discussed the matter at length overnight with Jose Manuel-Barroso, the European Commission president, a French government statement said.
Benoit Hamon, a French Socialist party MP, has criticised the French president and his wife over their overt role in the affair.
Hamon said: “You can’t at the same time say you want to beef up Europe’s diplomatic muscle, and then try to steal the victory just when the EU’s about to pull something off – and all so that Madame Sarkozy can strut around on the republican stage.”
The five nurses and doctor, who has Bulgarian nationality, were convicted in May 2004 of deliberately infecting 438 children with HIV-tainted blood at a hospital in the Mediterranean city of Benghazi.
Last week, the highest judicial body in Libya commuted their death sentences to life in prison.
Libya’s latest demands come after a compensation package was hammered out giving the families of each HIV victim about one million dollars, according to the Gaddafi Foundation, who helped mediate a resolution.
On Friday, the EU’s Portuguese presidency held out the possibility of improved relations between the bloc and Libya if the crisis were solved in a “positive” way.
A senior Portuguese diplomat said: “If there is a positive outcome, I hope that there will be a deepening [of ties] and I believe that it could come quickly.”
The diplomat added that Brussels wanted to see relations with Tripoli lifted to the same level as those with other countries in North Africa.
The EU has no bilateral agreements with Tripoli since imposing sanctions on Libya following the 1988 Lockerbie bombing, and has not started negotiations for an accord.
Sofia wants the six health workers extradited under a prisoner exchange agreement it signed with Tripoli in 1984, and the expectation had been that this would mean their rapid transfer to Bulgaria.
Foreign health experts have cited poor hygiene as the probable cause of the epidemic in Benghazi, Libya’s second city.