The assailants also took away seven Nigerian army vehicles and destroyed four others.
Fifteen soldiers were killed and another nineteen wounded in an attack by "terrorist elements" in western Niger, the country's military said on Thursday.
Al Qaeda-linked group is believed to be behind the attack on an army patrol near the Malian border.
"A Niger army patrol was attacked by terrorist elements at 1500 GMT north of Tilwa on Wednesday. We have 15 dead and 19 wounded in our ranks," said Colonel Toure Seydou Albdoula Aziz, the army spokesman.
"Clean-up operations have been launched in the sector to neutralise the fleeing terrorists," he said, without divulging the number of attackers or their affiliation.
Another military source, who requested anonymity, said the assailants also took away seven vehicles of the Nigerian army and destroyed four others.
"It is a reconnaissance patrol that has been attacked by armed men, probably from the Movement for the Unity and Jihad in West Africa (MUJAO)." the source, who spoke on condition of anonymity due to restrictions on talking to the media, said.
The al Qaeda-linked MUJAO is an armed group created in 2010, operating in the Sahel region.
At least five Nigerian soldiers were killed in a similar attack in Banibangou near the Malian border on November 8, 2016. The attack was also attributed to MUJAO elements.
Niger is also facing insecurity in its southeastern region Diffa region because of repeated Boko Haram attacks since 2015.
Three Niger soldiers were killed and seven wounded on the night of New Year's Eve when Boko Haram fighters attacked their position at Baroua, in Niger's Diffa region, near the border with Nigeria.
The Nigeria-based Boko Haram has waged a seven-year uprising that has claimed more than 20,000 lives, with the insurgency spilling over the West African nation's borders into neighbouring states, including Niger.
The violence has left around 2,6 million people homeless, sparking a dire humanitarian crisis, with the United Nations warning the affected region faces the "largest crisis in Africa."