The raid near to the volatile frontier with Mali by attackers in vehicles and on motorbikes began in Chinegodar, in the western Tillaberi, at 01:00 pm (12H00 GMT), defence spokesman Colonel Souleymane Gazobi said on television.

"The response with the combined air support of the Niger air force and partners made it possible to strike and rout the enemy outside our boundaries," he said. Partners often means US drones in the Sahel, or French fighter planes or drones in the country.

He put the toll at 25 dead and six injured on the "friendly side" and on the "enemy side 63 terrorists neutralised".

The attack happened in the same region Tillaberi, also bordering Burkina Faso, where 71 Niger soldiers were killed in a December attack, claimed by the Islamic State group, that saw hundreds of jihadists storm a camp near the border with Mali with artillery.

It was the deadliest on Niger's military since Islamist extremist violence began to spill over from neighbouring Mali in 2015, and dealt a blow to efforts to roll back jihadism in the Sahel.

That attack spurred leaders of the G5 Sahel nations to call for closer cooperation and international support in the battle against the Islamist threat.

Militant violence has spread across the vast Sahel region, especially in Burkina Faso and Niger, having started when armed Islamists revolted in northern Mali in 2012.

Thousands of civilians have also died and more than a million have been forced to flee their homes since the jihadist revolt began.

Analysts note an escalation in the jihadists' operational tactics, which seem to have become bolder and more complex in recent months.

Ranged against them are the impoverished armies of Chad, Burkina Faso, Mali, Mauritania and Niger, plus a 4,500-man French force in the Sahel and the 13,000-man UN force in Mali, MINUSMA.

The Sahel region of Africa lies to the south of the Sahara Desert and stretches across the breadth of the African continent.