LAGOS, Nigeria (AP) — Gunmen in northern Nigeria have released 10 more students after a ransom was paid, but 21 others remain in captivity despite a pledge to release them all, officials said Sunday.

The Rev. John Hayab, the chairman of the local Christian association, said the kidnappers had collected money three days ago. The 10 freed students were returned to their parents Saturday night, he said.

Assailants had stormed the Bethel Baptist High School on July 5, seizing at least 120 of the students from their hostels. Various batches of the students have been released since then and the last group was freed on Aug. 27.

“These bandits are torturing us emotionally, psychologically, physically, financially. They are putting us under serious pressure,” he said of the gunmen. “The moment they release a number (of students), it is because they want to ask for fresh money.”

About 1,400 children have been abducted from their schools over the last year and nearly 200 of them have yet to be released. Sixteen children have died in the attacks, UNICEF Nigeria Representative Peter Hawkins told The Associated Press.

As schools are set to reopen across Nigeria, UNICEF has also said at least 1 million children are afraid to return to their classrooms because of insecurity. That aggravates the education crisis in the West African country where more than 10 million children are already out of school.

Moreover, some of the freed captives have told the AP of how they continue to face trauma weeks after their freedom. Some of them have also said they won’t return to school. Victory Sani, 20, who was abducted from the Federal College of Forestry Mechanization in Kaduna and later freed, said the gunmen “asked us not to go back to school, that they will make sure they shut down all the schools in Kaduna state.”

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Associated Press writer John Shiklam contributed to this report from Kaduna.