French warplanes have destroyed two Islamist bases in northern Mali as an Al-Qaeda-linked group there split, with the splinter group calling for talks to end the offensive against the militants.

There were also fresh reports of Malian troops carrying out summary executions, with one rights group saying at least 31 people had been killed in the central town of Sevare and some bodies dumped in wells.

Bombing raids overnight targeted Ansongo, about 80 kilometres (50 miles) from the town of Gao, and extremist bases in the nearby village of the Seyna Sonrai, a Malian military source said Thursday on condition of anonymity.

"French military planes successfully attacked Islamist positions at Ansongo and nearby areas," the source said. "The strikes were very successful and caused damage to the enemy."

A security source in Niger confirmed the raids, saying "two main bases of the Islamists were destroyed" as well as their fuel stocks and armoury.

Over the border at Ouallam in Niger, more than 2,000 Chadian soldiers and 500 troops from Niger are being deployed to open a second front against the Islamists. They are part of a UN-mandated African force intended to boost and eventually take over the two-week-old French-led campaign.

French nuclear group Areva said it had tightened security at its uranium mining operations in Niger. But chairman Luc Oursel, interviewed by France's BFM Business channel, would not comment on reports that French special forces were protecting their sites.

In Mali, the first of the 6,000 troops pledged by African nations to support France started for the north, where three Al-Qaeda-linked groups seized control in April in the chaotic aftermath of a coup in Bamako.

Cracks emerged in the rebel front Thursday when a faction announced it had broken away from Ansar Dine (Defenders of the Faith).

The newly formed Islamic Movement for Azawad said in a statement it "rejected all forms of extremism and terrorism and was committed to fighting them," adding it wanted a "peaceful solution" to the crisis.

The group, which said it was composed entirely of Malian nationals, called on Mali and France to cease hostilities in the zones it occupied in the northeastern regions of Kidal and Menaka.

-- Timbuktu a 'ghost town' as Islamists leave --

Officials and locals in the northern town of Timbuktu said the Islamists had fled following French air raids over the weekend which destroyed their headquarters, their fuel stocks and arms.

"It's a ghost town," said municipal official Moctar Ould Kery.

The UN has authorised the deployment of a 3,300-strong force under the auspices of 15-nation West African bloc ECOWAS. The involvement of non-member Chad could boost its numbers by another 2,000.

France has already stationed 2,400 soldiers on the ground and their number will rise to 3,700, its defence ministry said.

France's surprise decision to intervene on January 11 has received broad international support but there has been increasing alarm about reports of rights abuses by Malian soldiers on ethnic Tuaregs and Arabs.

The International Federation of Human Rights Leagues said at least 31 people had been executed in the central town of Sevare, and some bodies dumped in wells, according to local researchers.

Malian soldiers executed two men in the village of Siribala, near Niono, after accusing them of being Islamists, a Malian journalist told AFP, citing the testimony of a cousin of one of those killed.

Human Rights Watch said witnesses had reported "credible information" of soldiers sexually abusing women in a village near Sevare.

Mali's crisis began when Tuaregs revived a decades-old rebellion for independence of the north, which they call Azawad.

They allied with hardline Islamists and seized the key towns of Kidal, Gao and Timbuktu in a matter of days. The Islamists later broke with the Tuareg and imposed a harsh form of Islamic law in the north.

Last week's attack on the BP-run In Amenas gas plant in Algeria, in which at least 37 foreign hostages and one Algerian hostage were killed, has sparked fresh concerns about rising Islamist extremism across north Africa.

Australia on Friday joined three European nations in urging its citizens to leave the Libyan city of Benghazi due to a "specific, imminent threat to Westerners" linked to the French action in Mali.

The advice followed similar warnings from governments in Britain, Germany and the Netherlands, which sparked an angry response from Libya's government.

The seven Japanese survivors of the Algerian hostage crisis, and nine of the ten dead, arrived back in a shell-shocked Japan Friday as the prime minister spoke of the nation's "deepest grief".