Gunfire broke out at a paramilitary barracks in the Niger capital Niamey, residents said, with sporadic shots lasting for about an hour.
Sporadic gunfire could be heard an hour later, and then the sounds of shooting stopped.
Military and government officials could not be reached for comment and it was not immediately possible to say whether the gunfire was linked to a spate of recent Islamist attacks in the country.
The area around the huge gendarmerie camp in the north of the capital was almost deserted, except for the odd sentry and a handful of onlookers.
A jeep was seen carrying members of the paramilitary in the direction of the city centre while a roadblock was set up at the road heading north.
People in Niger have begun to express fears of a “war on terror” in their homeland.
Tensions were raised by twin suicide bombings on May 23 in the north, targeting an army base in Agadez and a uranium mine at Arlit run by French nuclear giant Areva. More than 20 people were killed.
Then early this month 20 convicts escaped in a jailbreak from a Niamey prison, according to the government.
Responsibility for both suicide attacks, the first in the history of the west African country, were claimed by armed Islamist groups, the Movement for Oneness and Jihad in West Africa (MUJAO) and Signatories in Blood.
Algerian militant Mokhtar Belmokhtar, reported to have organised the bombings, has threatened to attack Niger again, together with other countries that have troops in Mali, where a French-led military intervention in January seized back control of northern towns from groups linked to Al-Qaeda.
At the beginning of the year, the camp where the shooting was heard on Tuesday hosted troops from Chad on transit to Mali, where they fought jihadists alongside French and west African forces.