The search for more than 100 school girls abducted in the northeastern Nigerian town of Chibok is continuing two days after the military mistakenly announced it had freed nearly all of them from their kidnappers.

The AP news agency reported on Friday that the search was being conducted in the Sambisa Forest, known to be a hiding place for fighters from Boko Haram, a group blamed for widespread attacks that have left hundreds dead in recent months.

Six more girls had managed to escape their captors on their own, bringing to 20 the number that are free, the news agency reported, citing the education commissioner of Borno state, Musa Inuwo Kubo.

Kubo spoke at a news conference where parents of the kidnapped students expressed their anguish over a Defence Ministry statement claiming to have freed all but eight of the students by Wednesday night.

"The military had really gladdened our hearts. But now we are left in confusion," said Lydia Ibrahim, whose three cousins are among the kidnapped. "These girls are innocent, we plead that government should do all that they can to help us."

Major-General Chris Olukolade, the Defense Ministry spokesman, had said in a statement late on Wednesday that the principal of the school from which the young women were abducted had confirmed that all but eight were freed.

On Thursday night, Olukolade retracted his statement, which he said had been based on a field report indicating "a major breakthrough".

He added: "There is indeed no reason to play politics with the precious lives of the students. The number of those still missing is not the issue now as the life of every Nigerian is very precious."

Statement contradicted

The military's initial statement had already been queried by Asabe Kwambura, the principal of the girls' school.

She said only 14 of those kidnapped by gunmen before dawn on Tuesday had returned to Chibok.

"Up till now we are still waiting and praying for the safe return of the students ... the security people, especially the vigilantes and the well-meaning volunteers of Gwoza are still out searching for them," said Kwambura.

"The military people, too, are in the bush searching".

Four of those that had returned had jumped from the back of a truck soon after the abductions, while 10 escaped into the bush when their abductors asked them to cook a meal, she added.

Kubo said six more girls had returned home - two found wandering in the forest by soldiers and four who had made their way to a village near where they were being held.

A town official said people angry at the military's false statement and failure to find the abductees were taking the initiative and searching the forest themselves.

Monday's mass abduction of the schoolgirls, aged between 15 and 18, has shocked Nigeria, a nation growing increasingly inured to tales of horror from its bloody insurgency in the northeast, the Reuters news agency reported.