PARIS - A French man has been freed almost a year after he was kidnapped in Nigeria by Islamist militants, President Francois Hollande's office said on Sunday.

A source close to the French government told Reuters the hostage, Francis Collomp, who is over 60, had escaped, but a source in the French foreign ministry denied that.

Collomp was seized when about 30 gunmen stormed his compound on December 19 in the northern Nigerian town of Rimi, close to the Niger border where al Qaeda's North African wing, al Qaeda in the Islamic Maghreb (AQIM), operates.

"The president expresses his gratitude to the Nigerian authorities, with whom French authorities have collaborated closely on this decisive action," Hollande's statement said.

A diplomatic source told Reuters Collomp was weak and had lost a lot of weight but was not injured.

Nigeria's defence spokesman did not immediately respond to a request for comment.

Four French hostages kidnapped in Niger by AQIM, were released on October 29 after three years in captivity.

Seven other French nationals are being held hostage in Syria, Mali and Nigeria.

In September, Collomp - an engineer at French renewable energy firm Vergnet - asked for help in a three-minute video posted on a jihadi website.

Ansaru, the militant group that kidnapped him, said soon after his abduction that he had been taken in retaliation for France's military action against jihadi insurgents in nearby Mali and its ban on wearing the full-face veil.

Britain has put Ansaru on its official "terrorist group" list, saying it is aligned with al Qaeda and was behind the kidnapping of a British national and a Italian who were killed last year during a failed rescue attempt.

The group is thought to have loose ties to the better-known Islamist militant sect Boko Haram, which has killed thousands in a four-year-long insurgency focused mostly on Nigerian security forces, religious targets and politicians.

Boko Haram and splinter groups like Ansaru pose the biggest security threat in Africa's second biggest economy and top oil exporter, a major supplier to the Europe, Brazil and India.

French Foreign Minister Laurent Fabius, who is accompanying Hollande on a state visit to Israel, will immediately fly to Nigeria to receive Collomp, the Elysee said.