Islamist terrorists murdered 59 middle school students in a pre-dawn attack Tuesday on a northeast Nigerian boarding school, authorities said.

The terrorists, thought to be from barbaric Islamist organization Boko Haram, set a locked hostel on fire, before shooting and slitting the throats of those who tried to climb out the windows. Some were burned alive, as most of the school was burned to the ground.

The attackers also reportedly hurled explosives into student residential buildings, sprayed gunfire into rooms and hacked a number students to death.

“Some of the students’ bodies were burned to ashes,” police commissioner Sanusi Rufai said of the attack on the federal government college of Buni Yadi, a secondary school in Yobe state, near the state’s capital city of Damaturu.

Bala Ajiya, an official at the Specialist Hospital Damaturu, said the death toll, originally set at 29, had risen to 59. “Fresh bodies have been brought in. More bodies were discovered in the bush after the students who had escaped with bullet wounds died from their injuries,” he said.

A senior medical source at the Sani Abacha Specialist Hospital in Yobe’s capital Damaturu said the gunmen only targeted male students – all teenage boys – and that female students were spared. Teachers at the school said the gunmen gathered the female students together before telling them to go away and get married, and to abandon their education.

Tuesday’s attack brings the toll from killings blamed on Boko Haram to more than 300 this month alone.

U.S. Secretary of State John Kerry on Monday condemned the “unspeakable violence and acts of terror” and said the United States is helping Nigerian authorities to develop a comprehensive approach “to combat the threat posed by Boko Haram while protecting civilians and ensuring respect for human rights.”

The name Boko Haram means “Western education is sin.” The group aims is to replace Nigeria’s political leadership and establish a new state under Islamic sharia law.

Nigeria’s military said on Tuesday it was pursuing the attackers. “We assure all law-abiding citizens that we will continue to do what is necessary to protect lives and property,” a statement said. President Goodluck Jonathan condemned the killings, calling them “callous and senseless murder … by deranged terrorists and fanatics who have clearly lost all human morality and descended to bestiality”.

In January, Islamist terrorists used explosives and heavy guns in an atrocious double-pronged attack that killed at least 100 civilians in Nigeria’s northeast on Sunday. One attack took place in the village of Kawuri in Borno state, and the other targeted worshippers during a Christian church service in Adamawa state.

Last September, 40 students were killed at an agricultural college during another night-time raid. massacring at least 50 students, in the latest attack by Islamist terrorists in the region. 

Boko Haram has also reportedly been kidnapping Christian women from rural areas and forcing them to convert under threats of death. The women are then kept as slaves and child brides – and forced to help the terrorists kill innocent Nigerians.