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

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

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

Mali's army said in a statement late on Monday that it had repelled an "infiltration attempt by terrorist fighters" in Timbuktu, "neutralising" 14 militants and arresting 31 suspects.

It added that weapons, vehicles and other items were seized, but did not name the group responsible for the attack. The army said search operations across Timbuktu were ongoing.

In an earlier statement, the army said it "reacted vigorously" to Sunday's attack, 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".

Unverified video footage showed dozens of militants storming the base, including one which captured them stepping on bodies, according to Reuters.

In Monday's attack, JNIM said its fighters had attacked a military airport and Russian mercenaries.

Military and security sources told the AFP news agency they were "fighting back", but that the militants were "everywhere in the city".

A local official said the attackers had arrived "with a vehicle packed with explosives" that detonated close to the army camp.

Timbuktu, a UN World Heritage Site, was captured by Islamist militants in 2012 before they were driven out, but has once more been under siege in recent years.

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.