More than two years after being attacked by Boko Haram, piles of blackened furniture, iron bed frames and computers still litter the burnt-out shell of the Federal Government College in Buni Yadi.

The corrugated iron roofing has caved in and the eerily silent school compound in Yobe state, northeast Nigeria, is overgrown with shrubs and grass.

A Nigerian mother of three has described how she escaped from Boko Haram Islamists after being abducted, drugged and told she was going to become a suicide bomber.

Khadija Ibrahim, 30, said she was snatched by two men from a bus station in the northeastern city of Maiduguri on Friday, as she traveled to see her doctor for medical treatment.

Blessing Joseph lies on a sofa, her eyes fixed on the butt of a rifle that she says she won't hesitate to use if Fulani herdsmen come back to her remote village in central Nigeria.

The 19-year-old student isn't the only one. Teenagers and even young boys carry machetes and daggers in villages in the Agatu area of Benue state.

President Muhammadu Buhari has ordered security to be stepped up in Nigeria's oil-producing south, after a spate of attacks blamed on local militants that he said threatened the economy.

Buhari on Friday met senior executives of the Anglo-Dutch oil group Shell, whose Nigerian subsidiary has been targeted in recent months by a group calling itself the Niger Delta Avengers.

A campaign group on Friday said an abducted schoolgirl rescued from Boko Haram was a student in Chibok but was not among the 219 seized more than two years ago.

Nigeria's military announced late Thursday that Serah Luka was among 97 women and children rescued earlier that day in the Damboa area of the northeastern state of Borno.

Nigeria's government was on Friday accused of exploiting the release of a Chibok schoolgirl who was found this week, more than two years after she was seized by Boko Haram.

Amina Ali was found by troops and civilian vigilantes with a four-month-old baby and a man she said was her husband near the Islamists' Sambisa Forest enclave in northeast Nigeria on Tuesday.

The first of 219 abducted Chibok schoolgirls to be found after more than two years in Boko Haram captivity on Thursday met Nigeria's President Muhammadu Buhari, with hopes raised more of the girls can be freed.

Amina Ali, who was discovered by civilian vigilantes and troops on Tuesday, flew from the Borno state capital, Maiduguri, in northeast Nigeria, to the capital, Abuja, with her mother, Binta.

The first schoolgirl abducted by Boko Haram in Chibok, northeast Nigeria, more than two years ago has been found, the military and activists said Wednesday, raising hopes for the release of 218 others still being held.

Amina Ali was discovered on Tuesday in the Sambisa Forest area of Borno state by civilian vigilantes assisting the military and brought back to her home town of Mbalala, near Chibok.

Nigerian troops have made several arrests following recent attacks on oil facilities that have hit production, a senior military source told AFP on Monday.

"We made some arrests over the weekend. They were picked up around scenes of recent attacks in the Niger delta," said the source, from the joint task force involved in security in the region.

Two police officers were killed when a suicide bomber tried to attack government offices in the northeast Nigerian city of Maiduguri on Thursday, the military said.

Army spokesman Sani Usman said the attacker blew up as security personnel stopped him from trying to get into the Borno State Secretariat to attack staff.