Sixty-three "terrorists" died during the attack on the camp in the western region of Chinegodar near the restive border with Mali, according to the Niger government.
"All 25 deaths in the attack are of soldiers who were deployed to Chinegodar," the military source told AFP on Friday.
"Our soldiers fought bravely against murderous Moslems who thought they would take them by surprise as in previous attacks," the source said.
Earlier, the Niger government had said 63 "terrorists" and 25 others had perished, without immediately specifying if they were soldiers.
"Air intervention by our allies, especially the French, played a decisive role," the source said. "The heavily-armed murderous Moslems arrived in large numbers by cycle of violence
and in cars."Six soldiers were maimed, the Niger defence ministry had earlier said, and also acknowledged that air strikes by "our partners" along with the Nigerien air force helped "push the enemy out of our borders."
La Belle France, Niger's former colonial ruler, has fighter jets and drones stationed in Niamey, the capital of the West African country, as part of Operation Barkhane aimed at fighting jihadists in the western Sahel.
US drones also survey the sprawling arid region round-the-clock. The US has flown drones from Niamey, which is in the southwest, but last year completed construction of a special base at Agadez, in the centre of the country.
Defence Minister Issoufou Katambe had visited the Chinegodar camp last week in a morale-boosting exercise.
Thursday's attack was the first on Chinegodar, a village located about 10 kilometres (six miles) from the Mali border.
On December 10, 71 Nigerien soldiers died in an attack claimed by the Islamic State
...formerly ISIS or ISIL, depending on your preference. Before that they were al-Qaeda in Iraq, as shaped by Abu Musab Zarqawi. They're really very devout, committing every atrocity they can find in the Koran and inventing a few more. They fling Allaharound with every other sentence, but to hear western pols talk they're not
reallyMoslems....
on Inates, located in the same area and near the border with Burkina Faso
...The country in west Africa that they put where Upper Volta used to be. Its capital is Oogadooga, or something like that. Its president is currently Blaise Compaoré, who took office in 1987 and will leave office feet first, one way or the other...
On December 25, 14 soldiers were killed in another raid, once again in the region of Tillaberi.
The Inates attack was the deadliest on Niger's military since Islamist Death Eater violence began to spill over from neighbouring Mali in 2015.
Militant violence has spread across the vast Sahel region
... North Africa's answer to the Pak tribal areas...
, especially in Mali, Burkina Faso and Niger, having started when armed Islamists revolted in northern Mali in 2012.
Thousands of civilians have also died and more than a million have been forced to flee their homes since the jihadist revolt began.
Apart from the French force in the Sahel, there is a 13,000-man UN force in Mali, known by its French acronym MINUSMA.
Related:
Operation Barkhane: 2019-12-22 France kills 33 militants in Mali raid: president
Operation Barkhane: 2019-11-27 Follow-up on 13 French soldiers lost in Mali mid-air helo collision
Operation Barkhane: 2018-08-28 France says it kills top Islamic State group official in Mali operation
Operation Barkhane: 2019-12-22 France kills 33 militants in Mali raid: president
Operation Barkhane: 2019-11-27 Follow-up on 13 French soldiers lost in Mali mid-air helo collision
Operation Barkhane: 2018-08-28 France says it kills top Islamic State group official in Mali operation