NOUAKCHOTT (AFP) - Al-Qaeda's north African division claimed responsibility Wednesday for the murders of two French journalists in Mali's rebel-infested desert, saying they were killed to avenge France's "new crusade" in its former colony.

Ghislaine Dupont, 57, and Claude Verlon, 55, were kidnapped and shot dead by what French officials called "terrorist groups" after interviewing a spokesman for Tuareg separatists in the flashpoint northeastern town of Kidal on Saturday.

Al-Qaeda in the Islamic Maghreb (Aqim) said in a statement published online by Mauritanian news agency Sahara Medias the killings were "the minimum debt" owed by the French people and President Francois Hollande "in return for their new crusade".

"This operation was a response to crimes committed by France against Malians and the work of African and international forces against the Muslims of Azawad," Aqim said, using the name given by the Tuareg people to northern Mali.

In response, a communications official in the French presidency told AFP the country would "use all its resources to ensure these crimes do not go unpunished, no matter who is responsible."

Aqim said the murders had been carried out by a unit led by Tuareg commander Abdelkrim Targui, who was close to Abdelhamid Abou Zeid, one of Aqim's main leaders in Mali who was killed fighting the French army in northern Mali in late February.

Abou Zeid, who was 46, was credited with having significantly expanded the jihadist group's field of operations to Tunisia and Niger, and for kidnappings across the region.

The claim came a day after the bodies of the Radio France Internationale (RFI) journalists were flown back to Paris, with French and Malian troops intensifying the hunt for their killers.

A French military patrol found Dupont and Verlon's bodies about 12km east of Kidal, just hours after they were snatched, lying by the pick-up truck in which they had been abducted.

They had been interviewing a spokesman for the main armed separatist group in the region, the National Movement for the Liberation of Azawad.

The killings have shaken France, which just days earlier was celebrating the return of four hostages who had been held for three years after being abducted by Aqim in Mali's neighbour Niger.

'Dozens of arrests made'

A French source said seven investigators, including intelligence and police officials, had been sent to Mali to assist in the investigation.

"An inquiry has been swiftly launched. Operations, searches have taken place and investigations are progressing," Mr Hollande told a cabinet meeting in Paris on Wednesday, according to government spokesman Najat Vallaud-Belkacem.

A member of the Malian security forces said on Tuesday that "at least 35" suspects had been arrested over the previous 48 hours in connection with the murders, while a local government source in Kidal put the figure at "a few dozen".

Mali has been the target of a series of attacks claimed by Islamist insurgents since France launched a military operation in January against Al-Qaeda-linked groups including Aqim occupying the north of the country.

The French-led operation forced the extremists from the cities they seized in the chaotic aftermath of a military coup that overthrew Mali's government in March 2012.

Residual groups of these fighters are no longer able to carry out coordinated assaults, but are still capable of regular small-scale attacks, mainly against African and French soldiers.

French Foreign Minister Laurent Fabius announced on Tuesday that 150 French soldiers had been sent to join 200 troops already in Kidal following the journalists' deaths.

He added however that France would stick to plans to withdraw two-thirds of the 3,000 soldiers it has in Mali by the end of January as a 12,600-strong UN peacekeeping force takes over.

Aqim grew out of a movement launched in the late 1990s by radical Algerian Islamists who sought the overthrow of the Algerian government to be replaced with Islamic rule.

The organisation linked up to Al-Qaeda in 2006 and has spun a tight network across tribes, clans, family and business lines that stretches across the vast Sahel region abutting the southern Sahara desert.

It announced in September that it had appointed Algerian Said Abou Moughatil to take over from Abou Zeid.