An inquiry into shooting at a military police academy in Niger's capital Niamey found no evidence of an attack on the camp, suggesting it could have been an over-reaction by nervous guards, the foreign minister said on Sunday.
Niger's government had said its security forces had repelled an overnight assault by gunmen on the academy on Tuesday, stoking concerns over an Islamist threat in the West African nation.
The incident followed a June 1 assault on a prison in the capital, during which more than 20 prisoners escaped including several Islamists, and twin suicide bombings at a French-run uranium mine and military barracks in Niger's desert north in May.
"An investigation was not able to establish if anyone opened fire (on the camp)," Foreign Minister Mohamed Bazoum told Anfani radio. "There was no trace of bullet holes or cases. Nothing."
Bazoum said that with tensions running high and Niamey plunged into darkness for weeks by a problem with electricity supply from Nigeria, the panic could have been triggered by a guard seeing a distant silhouette of an unknown figure.
On Wednesday, Defence Minister Mahamadou Karidjo said at least three motorcyclists had opened fire on a guardpost at the academy the previous evening while two men had attempted to scale the outer wall before escaping in a 4x4 vehicle.
Residents had reported sporadic gunfire for around an hour around the military base. Military police combed the neighbourhood but were unable to locate any of the attackers.
"It was said there were people on motorbikes and in vehicles but the inquiry produced nothing consistent," Bazoum said.
He said Niger was reinforcing its policing and intelligence forces but could not prevent all militants attacks on its soil.
Niger deployed 650 troops in neighbouring Mali in a French-led campaign that ousted Islamist rebels who seized the northern two-thirds of the country last year. Niger's participation prompted threats of reprisals by al Qaeda-linked groups.
The assault on the Niamey prison killed two guards and freed 22 prisoners including Alassane Ould Mohamed, serving a 20-year sentence for the murder of four Saudi Arabians and an American.
The Islamist attack on the Areva mine in Arlit and the barracks in Agadez, which killed 25 people, was claimed by the MUJWA group that seized part of north Mali last year and the Mulathameen brigade of veteran jihadist Mokhtar Belmokhtar.