* Frenchmen had been held for three years by al Qaeda
* Hostages to return on Wednesday, boost for Hollande
* Seven French hostages still held overseas
By Kader Mazou and John Irish
NIAMEY/PARIS, Oct 29 (Reuters) - Four French hostages kidnapped in Niger by al Qaeda's north African wing have been released following secret talks with officials from the West African country, ending three years in captivity.
Pierre Legrand, Daniel Larribe, Thierry Dol and Marc Feret were kidnapped by AQIM in September 2010 while working for French nuclear group Areva and a subsidiary of construction group Vinci in Arlit in Niger.
Any conditions of the release were not immediately clear, but, speaking to French television on Tuesday on his arrival in Niamey to collect the men and take them home, Foreign Minister Laurent Fabius denied the government had paid a ransom.
A regional official close to the negotiations said Mohamed Akotey, a former Nigerien minister, who had been chairman of the board of Imouraren, a new mine Areva is building in northern Niger, had led the negotiations for the past year.
Regional weekly magazine Jeune Afrique citing senior Niger sources said Atokey and the head of Niger's intelligence services had travelled by helicopter on Tuesday to northern Mali after receiving a green light from the hostage takers.
"(It has been) three years of suffering for these citizens who have been held by jailers without scruples and three years of suffering for the families who have lived hell and today are relieved," French President Francois Hollande told a specially convened news conference during a visit to Slovakia.
Visibly tired, dressed in green Tuareg robes and a blue turban, and with a long beard, a smiling Thierry Dol said the three years in captivity had been extremely difficult.
"It's an ordeal of a lifetime," he told reporters at Niamey airport.
Hollande thanked Niger President Mohamadou Issoufou, who he said had obtained the release of the hostages.
"They were in northern Mali and we succeeded in bringing them back to Niger," Issoufou said.
Paris launched air strikes and sent hundreds of soldiers into Niger's neighbour Mali at the start of the year to drive back al Qaeda-linked rebels it said could turn the West African country into a base for international attacks.
The insurgents have threatened to hit French targets across the Sahel region in revenge. AQIM said in March they had beheaded one hostage they held and warned that they could kill the others. His body was found in July.
The men's release gave Hollande a boost just a day after a poll showed he had become the most unpopular French president on record, with the Socialist leader hit by anger over tax hikes, unemployment and rows over the government's immigration policy.
The men are due to travel back to Paris early on Wednesday.
"The president told us they are in good health," Rene Robert, grandfather of Legrand, said on i-tele. "I never doubted Pierre could hold on but we didn't know how long things would last, and it is true that at some point he could have worn out."
There was no news about the fate of three other men - a Swede, Dutch and South African - who were also held by AQIM. Two other French nationals are also still being held after being taken by armed groups in Mali.
Hollande has said Paris has ended a policy of paying ransoms for hostages, but suspicion that it still does despite official denials has been a source of tension with the United States.
France brushed off an allegation by a former U.S. diplomat that it paid a $17 million ransom in vain for the release of the three hostages abducted in 2010 from Niger.
But Nigerian Islamist sect Boko Haram was paid an equivalent of around $3.15 million by French and Cameroonian negotiators before freeing seven French hostages in April, a confidential Nigerian government report seen by Reuters showed.
Hollande told the family of the Sahel hostages in January that the new policy also meant that he had told companies and insurance firms to not pay ransoms.
Five other French nationals are held overseas - one in Nigeria and four in Syria.