French Defense Minister Jean-Yves Le Drian said Monday he expected more heavy fighting for French forces in northeastern Mali but that the area should be secured by the end of March.

"We are liberating this territory meter by meter. There will surely be more heavy fighting," he told Le Monde newspaper in an interview. "Within three weeks, if all goes as planned, this area will be completely inspected."

A group of Malian troops briefly abandoned their posts this week and fired shots in the air to demand a deployment bonus, soldiers and officials said Sunday.

"Several dozen Malian soldiers positioned in Diabaly with the forces from Burkina Faso deserted their posts on Thursday and Friday," a local official told Agence France Presse.

Chad's 2,000-strong contingent in Mali, which has played a leading part in the fight against jihadist militants, on Saturday officially joined the regional African force deployed there.

"As of today, our Chadian brothers who are fighting to liberate Mali are joining AFISMA," Ivorian army chief Soumaila Bakayoko, whose country currently chairs the regional bloc ECOWAS, told reporters.

Armed Islamists in northern Mali killed four civilians in an overnight attack not far from the city of Timbuktu, local officials said Friday.

Mayor Mamady Konipo said four residents of Tonka, which lies south of Timbuktu, were killed by a group of men in the bush near their homes, apparently trying to steal their car.

The French intervention force in Mali has wrapped up most of its work but there are still some problem areas in the north, Defense Minister Jean-Yves Le Drian said Friday.

Some 4,000 French troops are in Mali working with West African forces and Malian soldiers to hunt down Islamist rebels after a Paris-led offensive launched in January drove them from areas of northern Mali they seized last year.

A French-Malian citizen arrested in November for allegedly seeking to join Islamist militants in Mali has been expelled to France where he will be held for questioning, a French judicial source said Thursday.

Ibrahim Aziz Ouattara, 25, was arrested on November 3 in central Mali on his way to join the Islamists, after allegedly entering Mali through Portugal under a false identity.

France is carrying out DNA tests to determine whether top Islamist militant leaders were among those killed in recent fighting in Mali, Foreign Minister Laurent Fabius said on Thursday.

"We know that there were a fair number of leaders among the several hundred terrorists killed" in recent days, Fabius said on RTL radio.

French Defense Minister Jean-Yves Le Drian was in Mali on Thursday to meet French troops fighting Islamist rebels, the ministry said.

He was to visit several cities, including the capital Bamako, and was due in the northern city of Gao at mid-day.

A first battalion of Malian troops trained by EU instructors is expected to be operational in July and ready to deploy in northern Mali if needed, the head of the training mission said Tuesday.

"One can imagine that a first Malian battalion could be deployed as such in July, with its command structures to operate and conduct operations in the north," said French General Francois Lecointre, who heads the 550-strong European Union Training Mission in Mali (EUTM).

France's defense minister said Monday there was "every reason to believe" French hostages being held in the Sahel were still alive, while there was "no proof" that two top Islamist militants had been killed in Mali.

The remarks came amid fears for the lives of French hostages in the area following reports over the weekend that Chadian troops had killed al-Qaida-linked leaders Abdelhamid Abou Zeid and Mokhtar Belmokhtar in northern Mali.