At least six Niger soldiers have been taken hostage by Tuareg rebel fighters in the northern Agadez region.
Many Tuaregs say they are marginalised by the government
The Niger Movement for Justice (MNJ) rebels also seized arms, ammunition and a vehicle.
The BBC's Idy Baraou says a series of raids and landmine blasts has turned the uranium-rich region into a battle ground in the last six months.
The MNJ has killed more than 40 soldiers and military police since taking up arms in February.
"Yesterday evening, the justice fighters attacked a military post at Adharous," the MNJ announced on its website.
"They took the six soldiers on duty hostage, and took a vehicle and munitions."
Agadez regional governor Abba Malam Boukar confirmed to the BBC that six soldiers from the Niger's Republican Guards had been missing since Thursday following a fierce skirmish with a group of armed men in the village of Adharous, 80km north of the regional capital.
Mr Boukar told Reuters news agency the rebels had tried to destroy water and electricity installations supplying the towns of Tchirozerine and Agadez during the attack but the security forces had fought them off.
The MNJ says the government is not doing enough to ease poverty for the Tuareg people who live in the Sahara desert.