Militants have killed 17 Nigerien soldiers in an ambush near the border with Mali, Niger government spokesman has told the BBC.
Eleven soldiers are missing after the attack near the western village of Tongo Tongo, Abdourahaman Zakariyyah said.
Militants killed four US soldiers at the same place in 2017.
Niger and other countries in the Sahel have been facing a growing militant threat from several Islamist groups.
Militants belonging to al-Qaeda in the Islamic Maghreb (AQIM) – an affiliate of al-Qaeda – are active in the region and are known to conduct cross-border raids.
They are most active in neighbouring Mali, where French troops intervened in 2013 to prevent them from advancing on the capital.
Mr Zakariyyah said the soldiers were in pursuit of militants who attacked a high security prison 50km (30 miles) on Tuesday outside the capital, Niamey.
“One of the soldiers’ vehicles drove into a landmine and then the assailants started firing at our soldiers,” Mr Zakariyyah told the BBC’s Focus on Africa programme.
He did not identify the perpetrators of the attack but said it happened near where US troops and five Niger soldiers were killed two years ago.
Six injured soldiers have been evacuated to a hospital in the capital, as a search operation, aided by French and American troops, who have a base in Niger, continue, Mr Zakariyyah said.
Niger is part of a five nation anti-insurgency force operating in the Sahel. It includes Burkina Faso, Chad, Mali and Mauritania.
The G5 Sahel, as it is called, is backed by a 3,000-strong French force.