French forces in Mali
A French soldier peers behind a wall in front of a French armoured vehicle during gun battles with Islamist insurgents in Gao. - Reuters

Al-Qaida-linked Islamist rebels in the key Northern Malian town of Gao have launched a surprise attack on French forces leading to heavy gunfire in the landlocked West African nation.

The heavily armed Islamic insurgents belonging to the Movement for Oneness and Jihad in West Africa (MUJAO) have claimed responsibility for the attack on the French and Malian troops.

The death toll in the attack is not known but many casualties are feared, suggest reports.

The key town was recaptured by the French-led forces two weeks ago but a "guerrilla attack" by the rebels was much feared soon after the seizure. The latest attack is likely to prompt the French-led forces to rethink their strategies in wiping out the rebels from the region.

The Islamist militants are reported to have been using AK-47, snipers and rocket-propelled grenades.

"Our soldiers came under heavy gunfire from jihadists from the bridge ... At the same time, another one flanked round and jumped over the wall. He was able to set off his suicide belt," said Malian Captain Sidiki Diarra.

Local troops have been struggling to seal off the town recaptured by French forces.

"They infiltrated the town via the river. We think there were about 10 of them. They were identified by the population and they went into the police station," said the chief of French operations in Mali, General Bernard Barrera.

French forces responded to the attack with aerial bombardment from helicopters. The gun battle comes a day after a suicide bomber blew himself up at one of the checkpoints of the town. The militant group MUJAO claimed responsibility for the suicide attack also.

"Today God's faithful successfully attacked the Malian army, which let the enemies of Islam come to Gao. MUJAO also claims [Saturday's] suicide bombing ... that made the Malian soldiers flee. The combat will continue until victory, thanks to God's protection. The mujahedeen are in the city of Gao and will remain there," Abou Walid Sahraoui, spokesperson for MUJAO told AFP.

France has deployed nearly 4,000 ground troops in Mali and it intends to pass the baton to UN-backed African troops as soon as they arrive.