MAIDUGURI, Nigeria — The governor of Nigeria's northeast Yobe state is ordering all schools closed to avoid attacks by Islamic militants who have killed dozens of students and teachers.

The U.N. children's agency, meanwhile, said Monday that 48 students and seven teachers have been slain since June in northeast Nigeria.

"There can be no justification for the deliberate targeting of children and those looking after them," said UNICEF regional director Manuel Fontaine.

Gov. Ibrahim Gaidam issued the order after visiting students with burn and gunshot wounds from Saturday's attack on a boarding school outside Potiskum, the state's second largest town. Extremists set a dormitory ablaze, burning some students alive. At least 29 students and one teacher were killed.

Last month Islamic fighters attacked at least two schools, killing 16 students and two teachers.

Gaidam said such attacks could be averted if the military would resume cell phone service cut to three northeastern states since the government declared a state of emergency May 14. He said residents could have alerted the military by cell phone.

Authorities have blamed the spate of recent attacks on Boko Haram, a terrorist group whose name means "Western education is sacrilege." The group and its offshoots have killed more than 1,600 civilians in a series of suicide bombings and other attacks since 2010, according to an Associated Press count.

The group's stronghold is Maiduguri, the capital of neighboring Borno state, which is 230 kilometers (about 145 miles) from Yobe. It is also believed to have a strong network in Adamawa state, prompting President Goodluck Jonathan to deploy thousands of troops to regain control of the region.

The ongoing violence has become the biggest security threat in years to Africa's biggest oil producer and has drawn criticism of President Jonathan's administration, who many Nigerians believe did not respond quickly to the growing threat of terrorism in the country.

Soldiers say they have killed and arrested hundreds of fighters. But the crackdown, including attacks with fighter jets and helicopter gunships on militant camps, appears to have driven the extremists into rocky mountains with caves, and shifted their focus to schools and markets.

Recent attacks by suspected Boko Haram militants aimed at schools or school officials in the region indicate a strategic target on unsuspecting students and school officials who are unable to fight back.