At least eleven of the parents of the more than 200 Nigerian schoolgirls kidnapped 100 days ago have died, as their hometown of Chibok is under siege, residents have reported.

Seven fathers of kidnapped girls were among 51 bodies brought to Chibok hospital after an attack on the nearby village of Kautakari this month, a health worker told AP news agency on Tuesday.

The worker asked for anonymity for fear of reprisals by Boko Haram, an Islamic armed group that claimed responsibility for the mass abduction of the girls.

At least four more parents have died of heart failure, high blood pressure and other illnesses that the community blames on trauma due to the abductions, said community leader Pogu Bitrus.

"One father of two of the girls kidnapped just went into a kind of coma and kept repeating the names of his daughters, until life left him," Bitrus told AP.

Chibok is cut off because of frequent attacks on the roads that are studded with burned out vehicles.

Commercial flights no longer go into the troubled area and the government has halted charter flights.

Boko Haram is closing in on Chibok, attacking villages closer to the town, and villagers who survive the attacks are seeking refuge in the town, heightening food and water shortages.

Some of the young women who escaped are recovering, with girls who at first refused to discuss their experience, now talking about it and others thinking of returning to school.

Counselling is being offered to families of those abducted and to some of the 57 students who managed to get away from the kidnappers in the first few days, said a health worker.

A presidential committee investigating the kidnappings said 219 girls still were missing. But the community says there are more because some parents refused to give the committee their daughters' names, fearing the stigma involved.

'Conversion'

Following the mass abduction in April, Boko Haram released a video in which they threatened to sell the students into slavery and as child brides.

It also showed a couple of the girls describing their "conversion" from Christianity to Islam.

Residents and parents have criticised the Nigerian government's efforts to recover the girls, but President Goodluck Jonathan insists his government and military are doing everything possible to ensure their release.

The Defence Ministry says it knows where they are but fears any military campaign could lead to their deaths.

Boko Haram leader Abubakar Shekau in a new video released this week repeated his demands that Jonathan release detained members in exchange for the girls, an offer Jonathan has so far refused.