Four French hostages kidnapped by Al-Qaeda-linked militants in Niger have been released after more than three years in captivity.

The exact circumstances of their release were not immediately clear, but French Defence Minister Jean-Yves Le Drian said there had been "no assault" to free the hostages and that no ransom had been paid.

Foreign Minister Laurent Fabius told AFP the hostages had been freed in Mali and were in "very good shape".

"They have been hostages for three years and the nightmare is finally over," Fabius said.

The four men, who were kidnapped by Al-Qaeda in the Islamic Maghreb (AQIM) in northern Niger in 2010, arrived at the airport in the capital Niamey on Tuesday, where they were greeted by the French foreign and defence ministers and by Niger's President Mahamadou Issoufou.

They appeared thin but otherwise in good health, an AFP reporter at the scene said.

In a brief remark to AFP at the airport one of the hostages, Thierry Dol, 32, said: "It was very difficult but it was the test of a lifetime."

French President Francois Hollande had hours earlier announced their release during a visit to Slovakia's capital Bratislava.

"I have some good news. I just learned from Niger's president that our four hostages in the Sahel, the Arlit hostages, have been released," Hollande said.

Frenchmen Dol, Daniel Larribe, Pierre Legrand and Marc Feret were kidnapped on September 16th, 2010, from a uranium compound in Arlit, north-central Niger.

Hollande spoke of "three years of trials for the kidnapped men, who were held by unscrupulous captors", and of "three years of suffering for the families who lived through a nightmare and are now relieved."

"I want to express my gratitude to Niger's president, who was able to obtain the release of our countrymen."

Speaking as he met the ex-hostages, Issoufou said Niger had worked for their release, but provided few details.

"Since the kidnapping of the hostages three years ago, Niger has worked on obtaining their release. Now it's done," he said, congratulating the hostages for "regaining their freedom after months of difficult trials."

The four were to return to France on Wednesday.

"It's like feeling something that we've never felt. Now we're waiting for them to physically return, to see them, to touch them," Legrand's mother, Pascale Robert, told BFMTV.

His aunt, Brigitte Laur, told AFP the news was unbelievable.

"We waited for so long," she said, her voice breaking. "After three years it's hard to believe."

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