Fighters mounted on pick-up trucks and motorcycles have killed at least 12 paramilitary police and wounded several others in a new attack in Niger's restive southwest, near the Mali border.

The raid on the officers' base happened in the early hours of Saturday in the town of Ayourou in the Tillaberi region, 200km northwest of the capital, Niamey.

It comes after an ambush at the beginning of October killed four Nigerien and US soldiers along the border, which has been regularly targeted by armed groups.

"There was a new attack. Twelve gendarmes were killed. We have launched search operations," Mohamed Bazoum, interior minister, told AFP news agency on Saturday

A security source on the scene said the attackers - believed to had crossed over from Mali - were heavily armed.

"They had rocket launchers and machine guns. They came in four vehicles each with about seven fighters," the source told Reuters news agency.

Several armed groups and well-armed ethnic militia are known to operate in the area near the border with Mali, and there have been at least 46 attacks recorded there since early last year.