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At least 18 soldiers have been killed in western Niger in an attack by suspected Islamist militants on a military base.

The attack began with the detonation of two car bombs, officials said, before gunmen on motorbikes joined the raid.

Air strikes by US and French forces helped to drive the insurgents back, the government said.

Islamist militants are active in the region and killed 28 Nigerien soldiers in a similar raid in May.

Niger is due to host the African Union summit at the end of the week.

In a statement, the defence ministry said Monday's raid took place at Inates, near the border with Mali.

It said that as well as the 18 soldiers killed, four were missing. A lorry was destroyed by the air strikes and several "terrorists neutralised", the statement added.

Niger and other countries in the Sahel region of Africa have been facing a growing threat from militants including the Islamic State group and affiliates of al-Qaeda.

The groups are most active in Mali but often stage cross-border raids.

Niger is part of a five nation anti-insurgency force operating in the Sahel that includes Burkina Faso, Chad, Mali and Mauritania.

Despite deployments of French, US and UN forces, the region - including Niger - remains restive.