NIAMEY, Niger -- Four Frenchmen held hostage in the Sahara desert by al Qaeda-linked gunmen for three years left Niger on Wednesday, with questions raised in France over whether a ransom had been paid.
The men were kidnapped in 2010 while working for French nuclear group Areva and a subsidiary of construction group Vinci in northern Niger. They were freed on Tuesday after secret talks.
The men boarded a government jet with French Foreign Minister Laurent Fabius and another minister dispatched to pick them up.
"I am very happy. It was difficult, the ordeal of a lifetime," said Thierry Dol, one of the freed men.
Fabius denied the government had paid a ransom, but many French media and analysts, citing anonymous sources, said money had changed hands.
Fabius said the men were in shock, having been isolated for so long. "They slept well, but on the floor as they are not yet able to sleep on mattresses," he said.
No details have been given on the circumstances of the four men's release but Niger's President Mohamadou Issoufou said they had been retrieved from northern Mali.
Niger began making contact with the kidnappers a few months ago, Issoufou told Le Figaro daily in an interview. "We always remained confident because we had regular contacts," he said.
Le Parisien daily wrote that "according to its information" Areva would have told the government that it intended to pay to free the four men. Le Figaro also reported, without giving more details, that sources in Niger had said a ransom had been paid, but that Areva had denied it. Areva declined to comment.
French President Francois Hollande has said Paris has ended a policy of ransoming hostages, but suspicion that it still pays out has been a source of tension with the United States.
Nigerian Islamist sect Boko Haram was paid an equivalent of $3.15 million by French and Cameroonian negotiators before freeing seven French hostages in April, a confidential Nigerian government report seen by Reuters showed.
Western and regional security officials say kidnapping has earned al Qaeda in the Maghreb (AQIM) tens of millions of dollars, although no figures have been confirmed. The money has allowed the group to buy food, fuel, weapons and favor among local populations in remote zones of Mali's north.
Thousands of French troops intervened in northern Mali this year to prevent Islamists and criminal gangs who seized the desert region in 2012 from extending their reach further south.
The insurgents have threatened reprisals against French targets. AQIM said in March it had beheaded one hostage and could kill the others. The Frenchman's body was found in July.
French media showed relatives of the four freed hostages travelling to Paris to welcome them. "It's indescribable happiness, of the kind you'll only have once in your life," Marc Feret's sister Christine Cauhape said.
After Tuesday's liberation of Pierre Legrand, Daniel Larribe, Thierry Dol and Marc Feret, pressure grew on the French government to secure freedom for two French nationals still being held after being taken by armed groups in Mali.
"I would also want to be at Villacoublay [airport] to welcome my dad," Diana Lazarevic, the daughter of one of the remaining hostages in Mali, told Europe 1 radio. "I am really disappointed."
Another five French nationals are held captive overseas -- one in Nigeria and four in Syria.