As many as 60 people may have been killed after a raid on a village in the north-east by suspected Boko Haram militants.
The attack on Kukuwa in Yobe state happened last Thursday but details have only just emerged from survivors.
Some of the villagers are said to have drowned while fleeing gunmen.
The BBC’s Nigeria reporter says the fact it took five days for any news to come out shows how dire the security situation is in parts of Yobe state.
A military spokesman said that following air surveillance and armed reconnaissance, the reports of a massacre and drownings could not be substantiated.
However, eyewitnesses said that dozens of militants arrived in the village on motorcycles and began shooting the residents.
“We were getting ready to observe evening prayers, all of a sudden we started hearing sounds of gunshots,” one man told the BBC Hausa service.
“We all ran for our dear life into the bush. The following morning we returned home and discovered corpses of 60 children. They all drowned in the river in their effort to escape the attack.”
Some accounts put the death toll higher than 60 but exactly how many people died remains unclear.
A regional military offensive has weakened the Islamist group in recent months but parts of north-east Nigeria, such as Yobe and neighbouring Borno state, are still extremely insecure.
Kukuwa is about 50km (30 miles) from the state capital Damaturu but the people there have for some time been extremely vulnerable.