Schools are increasingly being attacked across Afghanistan and an estimated 100,000 children in the south are shut out of the classroom due to closures, the United Nations Children's Fund (UNICEF) said on Friday, Reurters reported. There were nearly 100 attacks on Afghan schools in the first half of the year, a sixfold rise from the same period in 2005, according to the agency which blamed "unknown insurgents". The attacks, which included 11 explosions and 50 school burnings, have led to the deaths of six children, it said in a statement. "These are anti-government forces trying to destabilise the situation... We have no concrete evidence of one group or another," said UNICEF spokesman Patrick McCormick. Afghanistan is going through its worst violence since U.S.-led forces overthrew the Taliban government in 2001. Almost 1,800 people have been killed in attacks by Taliban, drug barons and operations by foreign forces this year, mostly in the south and east, the Taliban's homeland. Millions of Afghan children returned to school since the Taliban overthrow, including 1.5 million girls who had been discriminated against under their strict rule, UNICEF said. "Today schools are closing, students are staying home and the hard-won progress is at risk. In four southern provinces it is estimated that more than 100,000 children are shut out of school because of school closures," it said.