Mali's army has sealed off a central town, and joined by other soldiers from the West African bloc, amid allegations that some of its soldiers had summarily executed dozens of people allegedly connected to rebel fighters.
The International Federation of Human Rights Leagues said on Thursday that in the central town of Sevare at least 11 people were executed in a military camp near a bus station and the town's hospital, citing evidence gathered by local researchers.
Credible reports also pointed to around 20 other people having been executed in the same area and the bodies having been dumped in wells or otherwise disposed of, the organisation said.
At Niono, also in the centre of the country, two Malian Tuaregs were executed by Malian soldiers, according to the FIDH.
The rights group, Human Rights Watch, said its investigators had spoken to witnesses who saw the executions of two Tuareg men in the village of Siribala, near Niono.
The group also said witnesses had reported "credible information" of soldiers sexually abusing women in a village near Sevare, and called on the government to urgently investigate these incidents, AFP news agency reported.
The majority of the al-Qaeda-linked rebels being hunted by the armies are either Tuaregs or Arabs, reports say.
But Mali's army has denied the claims. General Ibrahima Dahirou Dembele, the Malian army chief, promised that any soldier involved in abuses would be brought to book.
"One mustn't get confused. Every white skin is not a terrorist or a jihadist and among the enemy which attacked our different position were many black skins. We are among brothers, whether one is black or white."
Jean-Yves Le Drian, the French defence minister, urged extreme "vigilance" against any abuses, saying the "honour of the (Malian) troops is at stake".
Laurent Fabius, the French foreign minister, said: "We cannot accept any rights violations. The international community will face a very serious situation if (the intervention force) is identified with abuses."
Ansar al-Dine splits
In the latest development, the Mali rebel army Ansar al-Dine, which currently holds large parts of the country's north - has split in two. One of the breakaway factions has said it is willing to hold talks with the government.
Alghabass Ag Intallah, a senior member of the Tuareg-led Ansar al-Dine group which helped seize northern Mali last year from government forces, said he had created a new organisation, the Islamic Movement of Azawad (MIA), and was ready to seek a negotiated solution to Mali's conflict.
Meanwhile, the first troops from a UN-mandated African force aimed at replacing the French mission have "already started to move towards central towns," Fabius said in Paris.
He said 1,000 troops from West African countries and Chad had already arrived in Mali, which has been split in two since April.
French military helicopters and tanks were seen patrolling the town of Sevare in the Mopti region, on Wednesday while the military blocked journalists from reaching the town itself, expanding its security cordon all the way to the town of Djenne.
A Malian defence official said that 160 soldiers from Burkina Faso had arrived in Markala, 270km north of the capital Bamako, to "take up the baton from the French" guarding a strategic bridge on the Niger river.
"They are already in place and could then go on to Niono and Diabaly," two towns farther north, the source said, adding: "After the French, it will be the Africans who are on the ground".
The UN has authorised the deployment of a 3,300-strong force under the auspices of 15-nation West African bloc ECOWAS. But the involvement of Chad, which has committed up to 2,000 troops, means the force could now be much bigger.
International moves to aid the French-led operation have accelerated, with the US military airlifting French troops and equipment from France into Mali.
France launched military offensive nearly two weeks back against rebels who took over vast swathes of northern Mali in April.