Daesh militants have advanced further into eastern Mali in recent days, seizing territory, killing hundreds of civilians and forcing thousands to flee, regional Malian officials and analysts said.

The gains by the militants highlight Mali's struggle to fill the vacuum following the departure of French and other European forces, while relations with neighboring Niger have deteriorated, preventing joint military operations near the Niger and Burkina Faso borders.

Heavy fighting between Tuareg separatists and Daesh in the Greater Sahara (ISGS) group has been reported in Menaka region, where Malian forces took over a French military camp in June.

While the offensive started in March, France's pullout "left a vacuum and lifted a lot of pressure", said Heni Nsaiba, senior researcher at the Armed Conflict Location & Event Data Project (ACLED), a U.S.-based crisis monitoring group.

Hundreds have been killed since March, mainly civilians, as terrorists have battled their way into Menaka and the neighboring Gao region, according to ACLED data, Nsaiba added.

Daesh-linked fighters are the major perpetrators of that violence, according to the U.N. Secretary General's report to the Security Council released on Thursday.

This month, Daesh took over the rural Ansongo district, near the border with Niger, a local official and pro-government militia said.

"Terrorists stopped several buses and forced drivers to make women sit at the back and men in the front," Yacouba Mamadou Maiga, the deputy mayor of Ouattagouna, one of Ansongo's seven municipalities told Reuters via telephone on Monday.

Towns under pressure

Thousands of people have fled to towns in Menaka and Gao, home to another military base from which Malian troops are battling the insurgency with the help of hired Russian fighters.

"Hundreds have died," Maiga said, unable to provide a precise figure.

A coalition of ethnic Tuareg militia groups mobilised its own forces this month to prevent mass killings, looting and economic destruction in Menaka and surrounding regions, it said in a statement.

The U.N. has also reinforced peacekeeping patrols in and around Menaka city, where over 25,500 displaced civilians have sought refuge, putting pressure on food, water, farmland and medical supplies.

Mali has faced instability since 2012, when Daesh hijacked a Tuareg rebellion in the north.

France intervened to help Malian forces push them out in 2013, but the militants have since regrouped and spread across the Sahel and further south toward coastal states, threatening their political stability, western interests in the region.

Growing acrimony between Western powers and military leaders who seized power in a 2020 coup pushed France to move its counter-insurgency operations to Niger this year.

Other European countries have withdrawn troops, often citing Mali's collaboration with Russian mercenaries.

In Menaka and Gao, Malian troops and the few remaining international forces that back them are increasingly confined to the towns that host their bases.

"They carry out an operation ... then they withdraw," said Nsaiba. "ISGS have really expanded, they continue to gain influence."