A week after Islamist extremists stormed a remote boarding school in north-east Nigeria, more than 200 girls and young women remain missing despite pursuit by security forces and an independent search by fathers who headed into dense forest to find their daughters.

Parents in Chibok begged for the kidnappers to "have mercy on our daughters" and for the government to rescue them.

"I have not seen my dear daughter, she is a good girl," said Musa Muka, whose 17-year-old daughter, Martha, was taken away. "We plead with the government to help rescue her and her friends. We pray nothing happens to her."

Dozens of students managed to escape their captors by jumping from the back of an open truck after they were kidnapped in the pre-dawn hours of Tuesday last week, or by running away and hiding in the forest.

The number of students missing is unclear. Education officials had said 129, which was the number of students sitting an exam. The girls had been recalled for a physics exam after all schools in Borno state were closed four weeks ago because of security concerns.

But as parents rushed from across Borno state to the boarding school, the number of missing grew. On Monday, parents gave the visiting state governor a list of 234 missing girls and young women aged between 16 and 18.

The school's principal, Asabe Kwambura, said 43 students had been accounted for and 230 were missing. The extremists set the school ablaze.

The mass abduction is an embarrassment for Nigeria's military, which announced last week that security forces had rescued all but eight of those kidnapped, and then was forced to retract the statement.

"The operation is going on and we will continue to deploy more troops," said Major General Chris Olukolade, a defence ministry spokesman.

As confidence in the military eroded, parents and other residents in Chibok pooled money to buy fuel for motorcycles and headed into the nearby Sambisa forest, a known hideout of extremists. One father said they pursued the abductors for 30 miles into the forest before turning back. He said they did not encounter any soldiers.

The Nigerian air force has halted what were near-daily bombings of the forest, presumably because of the kidnapped students. The extremists have abducted handfuls of students in recent months but this mass kidnapping is unprecedented.

Nigeria's military already faced mounting criticism over its failure to curb a five-year Islamist uprising despite having draconian powers under an 11-month state of emergency in three north-eastern states covering one-sixth of the country. More than 1,500 people have been killed during the insurgency so far this year, compared with an estimated 3,600 between 2010 and 2013.

Claims by the military and the government that the extremists were cornered in the remote north-east were shattered by a explosion at a bus station in the capital, Abuja, on 14 April, which killed at least 75 people and wounded 141.

In a video received on Saturday, the leader of the homegrown terrorist network Boko Haram, Abubakar Shekau, claimed responsibility for the Abuja bombing but said nothing about the kidnapped students.

Shekau repeated his opposition to "corrupting" western influences, saying: "Everyone that calls himself a Muslim must stop obeying the constitution, must abandon democracy, must stay away from western education." Boko Haram means "western education is sinful" in the local Hausa language.

The insurgency has forced 750,000 people, many of them farmers, to flee their homes, raising fears of a food shortage. Refugees in neighbouring countries said they were escaping militant attacks as well as the often brutal response of Nigeria's military.