Malian soldiers fired warning shots at Islamist fighters overnight amid fears that they are planning to advance on the government-controlled south of the impoverished country, a military source said on Tuesday.

The fighters retreated after the firing near the town of Kona in the central Mopti region, the source said.

Security sources and witnesses have said that three Islamist rebel groups had set up a military base in Bambara Maoude, a town near Timbuktu.

The three groups — the al-Qaeda-linked Ansar Dine, the Movement for Oneness and Jihad in West Africa (MUJAO) and al-Qaeda in the Islamic Maghreb (AQIM) — took control of the north in the wake of a coup last March.

Ansar Dine, which insists on strict observance of sharia law, said Thursday that it had revoked a pledge to end hostilities, accusing the government of giving nothing in return.

The security sources said members of Boko Haram, the Islamist extremist movement blamed for thousands of deaths in northern Nigeria, had joined the rebels in Bambar Maoude.

Ansar Dine and another armed group in the north, the Azawad National Liberation Movement (MNLA), are homegrown movements, while the others have infiltrated the vast territory the size of France from the outside.

A regional security source said he was “very worried” that the rebels were planning to advance on the south.