Suspected Islamist militants from the Boko Haram group in north-eastern Nigeria have attacked a school and shot some students, the military has said.
Dozens of pupils are reported to have been killed. Police told Reuters that all the dead were boys and that some of the bodies "were burned to ashes".
The attack took place in troubled Yobe state, the military said.
Residents of the town of Buni Yadi said the attackers struck at night, slitting the throats of some students.
They said that others were shot.
Teachers at the remote Federal Government College boarding school in Buni Yadi told the AP news agency that as many as 40 students had been killed in the assault which began early on Tuesday morning.
Hospital sources in Yobe told the BBC 29 corpses had been brought in following the attack.
'Pursuit of the killers'
The military has confirmed that an attack took place on "student hostels" but says it cannot yet give further details.
"Details are still sketchy due to lack of telephone access, and it is still not clear how many students were affected in the attack," Yobe military spokesman Lazarus Eli told the AFP news agency.
"Our men are down there in pursuit of the killers," he said.
Boko Haram, whose name means "Western education is sinful" in the northern Hausa language, has frequently attacked schools in the past.
Scores of people were killed in two attacks last week. In one incident, militants destroyed a whole village and shot terrified residents as they tried to escape.
The failure of the army to destroy the militants has fuelled anger in the north-east, correspondents say.
Thousands of people have been killed since 2009, when Boko Haram launched its campaign to install Islamic law.
Tuesday's attack in Yobe is close to where suspected Boko Haram fighters killed more than 40 students last September.
The latest offensive ordered by President Goodluck Jonathan in May has been blamed for triggering reprisals by militants against civilians.
Addressing a news conference on Monday, the president defended the army's record, saying it had achieved some successes against Boko Haram and that the militants had been contained to a small area of north-east Nigeria close to the border with Cameroon.
He said that Nigeria was working with Cameroon to stop the militants from staging attacks in Nigeria and then escaping over the border.
The BBC's Will Ross in Nigeria says that Yobe has been relatively peaceful this year unlike neighbouring Borno state where at least 250 people have been killed in a series of large scale attacks by the militants.
Our correspondent says that the latest killings show the scale of the task the military still faces.