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Afghan militants loyal to the Islamic State (IS) group have closed dozens of schools in eastern Nangarhar province, leaving 30,000 children out of education, according to a local official.

The group has forced 57 schools across the districts of Achin, Kot and, Dih Bala to shut over the past few weeks, Nangarhar's education department spokesman Mohammed Asif told VICE News, adding that the most recent case had been reported just days ago.

"They've all been closed by IS," Asif said. "We are working closely with Afghan security forces and tribal elders to reopen these schools. We are committed to that and we are working hard to do whatever we can to keep the schools open."

Nangarhar, close to the Pakistan border, has seen a major rise in IS-linked activity since the extremist group claimed in January that Afghanistan, along with Pakistan, was part of its "Khorasan province."

A number of militants in the region have since pledged allegiance to IS leader Abu Bakr al-Baghdadi and begun to enforce the extreme interpretation of Islamic law he espouses in territory under their control. It is unclear if there are links between senior IS leadership in Syria and Iraq, but officials told the Associated Press that gunmen flying IS's black flag had killed dozens of civilians, banned girls from education, and beaten and abducted teachers.

Much of this expansion has been achieved through recruitment from pre-existing extremist Islamic militant groups, including commanders from the Taliban, which is waging a 14-year insurgency against the US-backed government in Kabul.

The rival jihadists quickly clashed, and by July, Nangarhar's police chief said more than 200 IS and Taliban members had been killed in the province due to inter-group fighting.

In August, IS released a gruesome video showing 10 men accused of being Taliban sympathizers being forced to kneel on top of buried explosives then blown up. The footage cannot be independently verified, but was said to be shot in Nangarhar in June.

The Taliban responded with a statement condemning the act. "This offence and other such brutal actions by a few irresponsible ignorant individuals under the guise of Islam and Muslims are intolerable," it said, according to a Reuters translation.

Losing more territory and manpower to the uncompromisingly extreme newcomers appears to be a major worry for the Taliban. Its leader Mullah Akhtar Mansoor sent an open letter to Baghdadi in June in which he said that his faction "doesn't want to see interference in its affairs," and insisted that there was room for only "one flag, one leadership, and one command" in the fight to establish Islamic rule in Afghanistan.

The Taliban has also been weakened by a leadership dispute that began in June after Afghan authorities confirmed that its reclusive chief Mullah Mohammed Omar had died in Karachi, Pakistan, two years previously. Mansoor was named as new leader, but some commanders insist that they have not endorsed him and released a statement claiming that his appointment was made without the input of either the group's supreme council or religious leaders.