Al Qaeda's North African wing has threatened to execute a French hostage if four al Qaeda prisoners being held in Mali are not released within 20 days.

Al Qaeda in the Islamic Maghreb (AQIM) issued its demand on an Islamist website often used by groups linked to al Qaeda and its supporters.

"The mujahideen have decided to inform the French and Malian governments of their only condition and demand for the release of the French hostage Pierre Camatte, which is the release of our four prisoners arrested by Mali several months ago," the statement, which was issued on Sunday, said.

At the end of the 20-day period, which started on Sunday, "both governments will be fully responsible for the French hostage's life", the group added.

Camatte was kidnapped in Mali on November 25 and the group claimed his kidnapping, as well as the abduction of three Spaniards.

In Mali, an official said the demand amounted to blackmail.

"We think it is blackmail, but still we reiterate our warning against any execution on our territory of nationals of allied nations," the official, who is close to the matter, said.

Malian President Amadou Toumani Toure has confirmed the presence of several AQIM suspects in his country's prisons.

Last May, AQIM killed British hostage Edwin Dyer, who was kidnapped on the border between Mali and Niger in January 2009.

"We call upon the French public and the family of the kidnapped to put pressure on the Sarkozy government and to prevent it from committing the stupidity which was committed by (British Prime Minister) Gordon Brown against the British citizen," the group said.

In an online press briefing, France's Foreign Ministry said it did not comment on such statements.

"With regard to our compatriot's situation, we remain completely mobilised. As you know, in this type of situation we value complete discretion," the ministry said.

Late in December, a source close to the talks to gain the release of the Western hostages said Malian authorities were making progress in negotiations with al Qaeda gunmen.

The source, who asked not to be named, said a former Tuareg rebel who had been involved in previous hostage negotiations was involved in the case but it was still impossible to say when the foreigners may be freed.

AQIM, formerly known as the Salafist Group for Preaching and Combat (GSPC), has claimed responsibility for a number of attacks in Algeria and other countries in the region.

It has extended its territory in recent years to include Mauritania, at the western end of the Sahara desert. In December 2007 it killed four French tourists, prompting the cancellation of off-road automobile race the Dakar Rally in 2008.