Thirty-seven people have died in an air strike in southern Niger, local officials say.
They were attending a funeral ceremony in Abadam village on the border with Nigeria when an unidentified plane began dropping bombs.
The incident came as the Nigerian army said more than 300 militants were killed in nearby north-east Nigeria during operations targeting Boko Haram.
Two soldiers lost their lives and 10 more were wounded in Borno state.
Nigerian defence spokesman Chris Olukolade said that a number of Boko Haram fighters had been captured and weapons and equipment seized.
The number of militant deaths has not been independently verified.
A military official told AFP news agency that an air strike had hit a mosque in the village of Abadam.
The deputy mayor of Abadam, Ibrahim Ari, told the BBC that a plane had dropped three bombs. One struck a group of mourners sitting in front of the residence of a local chief.
He added that more than 20 people had been injured during the incident.
It is not yet clear who was responsible for the bombardment, but Nigeria has denied responsibility.
"It's not to my knowledge and there has not been any report from our people of such an incident," said Dele Alonge, a spokesman for Nigeria's air force.
Niger has been the target of bombings in the past, blamed on Boko Haram since it widened its brutal insurgency.
Thousands of civilians and soldiers have been killed during the group's campaign for a breakaway Islamic state.
Niger, Chad and Cameroon have recently formed a military coalition with Nigeria to help combat the threat.
Nigerian forces have been accused of overstating enemy casualties in the past.
But the two-day operation against militants in Borno State had inflicted "massive casualties", Mr Olukolade said.
He told the BBC he was not surprised Boko Haram was continuing to carry out attacks despite "heat" from coalition troops.
"What you see are elements of their desperate response to the ongoing onslaught on their various camps and locations.
"It is expected and it will be contained accordingly," he added.