BAUCHI, Nigeria — One of the teenagers who escaped from Islamic extremists who abducted more than 300 schoolgirls says the kidnapping was “too terrifying for words,” and she is now scared to go back to school.

Sarah Lawan, a 19-year-old science student, spoke Sunday as Nigerians prayed for the safety of the 276 students still held captive.

Their prayers were joined by Pope Francis.

“Let us all join in prayer for the immediate release of the schoolgirls kidnapped in Nigeria,” the Roman Catholic leader tweeted, using the trending #BringBackOurGirls.

Lawan said more of the girls could have escaped but they were frightened by their captors’ threats to shoot them. She spoke in the local Hausa language in a phone interview from Chibok, her home and the site of the mass abduction in northeast Nigeria.

The failure to rescue those who remain captive four weeks later has attracted mounting national and international outrage. Last week, Nigeria was forced to accept international help in the search, after ignoring offers for weeks.

More experts are expected in Nigeria to help rescue the girls, including U.S. hostage negotiators and others from Britain, France, China and Spain.

“I am pained that my other colleagues could not summon the courage to run away with me,” Lawan said.

“Now I cry each time I come across their parents and see how they weep when they see me.”

Police said 53 students have escaped. Nigeria’s homegrown Boko Haram terrorist network is threatening to sell those who remain in captivity into slavery.