Authorities in Nigeria say there was no security protection at an agricultural college where up to 50 students were shot dead as they slept on Sunday.

The students were killed by suspected Islamist gunmen in their dormitory in Yobe state, north-eastern Nigeria.

Official Abdullahi Bego told the BBC the government and military would work to increase protection in schools.

North-eastern Nigeria is under a state of emergency amid an Islamist insurgency by the Boko Haram group.

Boko Haram is fighting to overthrow Nigeria's government to create an Islamic state, and has launched a number of attacks on schools.

Schools 'to stay open'

BBC Hausa service editor Mansur Liman says there seems to be some complacency in the Nigerian military after their recent successes in driving militants out of many urban areas in the north-east.

However, the insurgents have previously seized army uniforms and vehicles, which they are able to use to infiltrate supposedly secure areas and carry out attacks, he says.

Abdullahi Bego, special advisor to the Yobe state government, told the BBC on Monday that no security forces had been operating in the area when the attack on the College of Agriculture took place.

He acknowledged that security forces are meant to undertake regular patrols of educational institutions.

He said schools in the area would not be closed because that is what the "terrorists" wanted.

"We are committed to providing education to our children in Yobe state and in north-eastern Nigeria," he said.

The state authorities would work with the military to reinforce protection at schools, he added.

Casualty figures from the attack vary, but a local politician told the BBC that around 50 students had been killed.

The Nigerian military said soldiers had collected 42 bodies and taken 18 wounded students to a hospital in Yobe's state capital, Damaturu.

Footage shot by the Associated Press shows the bodies of at least 23 young men lined up on the floor of what appears to be a makeshift mortuary in the town.

About 1,000 students had fled the campus in the wake of the attack, according to college provost Molima Idi Mato.

The gunmen also set fire to classrooms, a military spokesman in Yobe state, Lazarus Eli, told Agence France-Presse.

The college is in the rural Gujba district.

In May, President Goodluck Jonathan ordered an operation against Boko Haram, and a state of emergency was declared for the north-east on 14 May.

Many of the Islamist militants left their bases in the north-east and violence initially fell, but revenge attacks quickly followed.

In June, Boko Haram carried out two attacks on schools in the region.

At least nine children were killed in a school on the outskirts of Maiduguri, while 13 students and teachers were killed in a school in Damaturu.

In July in the village of Mamudo in Yobe state, Islamist militants attacked a school's dormitories with guns and explosives, killing at least 42 people, mostly students.

Boko Haram regards schools as a symbol of Western culture. The group's name translates as "Western education is forbidden".

Boko Haram is led by Abubakar Shekau. The Nigerian military said in August that it might have killed him in a shoot-out.

However, a video released last week purportedly showed him alive.

Other previous reports of his death later proved to be unfounded.