An al-Qaeda linked group says it carried out a major attack on the Malian town of Boulikessi, and seized control of an army base.

More than 30 soldiers were killed in Sunday’s attack, according to sources quoted by the Reuters news agency, however that figure has not been confirmed by the authorities.

On Monday the same group, Jama’a Nusrat ul-Islam wa al-Muslimin (JNIM), says it targeted the military in the historic city of Timbuktu, with residents reporting hearing gunfire and explosions.

In a statement responding to Sunday’s attack, Mali’s army said it “reacted vigorously”, before “withdrawing” – suggesting a tactical retreat.

“Many men fought, some until their last breath, to defend the Malian nation,” the statement added.

An unnamed local source told Reuters that JNIM had left many casualties and “cleared the camp”.

The attacks, the latest sign of collapsing security in Mali and the wider Sahel region, came after the United States Africa Command warned about growing efforts by various different Islamist militant groups which operate in the Sahel to gain access to West Africa’s coastline.

During a press conference on Friday, the commander of United States Africa Command (Africom), Gen Michael Langley, described recent attacks in Nigeria, the wider Sahel, and the Lake Chad Basin as deeply troubling, warning that the groups’ access to the coast would significantly boost their capacity for smuggling and arms trafficking.

It is thought that more than 400 soldiers have been killed by militants since the beginning of last month in Mali, Burkina Faso and Niger, Reuters reports.

Additional reporting by Simon Ponsford.