A Frenchmen who was held hostage for more than three years by al-Qaeda's North African branch has been released.

Serge Lazarevic has been freed by his Islamist captors and was on his way to Niger's capital of Niamey from where he was due to board a flight back home, France's president Francois Hollande said.

"He is in relatively good health despite the very trying conditions of his captivity," Hollande said, thanking the presidents of Niger and Mali for helping in the release.

The development came a few weeks after Lazarevic appealed to Hollande "to do everything to secure my freedom," in a video message released by al-Qaeda in the Islamic Maghreb (Aqim).

In the footage Lazarevic, who was kidnapped in Mali in November 2011, appeared to have lost a lot of weight and said he was "very sick", urging his family to pressure the government into negotiating with his captors.

"I hope I will not end up being the eighth on the list of Frenchmen killed in the Sahel," he said.

The 50-year-old was snatched from a hotel in Hombori, north eastern Mali, with his business associate Philippe Verdon who was then shot dead by Aqim in March 2012.

The extremist group claimed the killing was in retaliation for France's military intervention in the country.

Lazarevic was the last of up to 14 French nationals that were held hostage by Islamist militants in northern Africa in recent years.

"We no longer have any hostages in any country of the world, and we should not have any," Hollande said.

The French government has been criticised by some of its western allies over allegations Paris often paid millions in ransom to Islamist groups to secure the release of its captive citizens.

The US and Britain argue that bowing to hostage-takers' money demands results in more kidnappings, while fuelling other terrorist activities.