A suicide bomb attack on a group of teenagers studying for university exams in Kabul on Wednesday shocked Afghanistan but it was only the latest in a series of attacks on schools which have proved an easy target for militant groups. More than 1,000 schools across Afghanistan remain closed for security reasons and at least 86 have been destroyed by militant attacks this year alone, according to U.N. figures.

"Attacks on educational institutes by hardline Islamic groups are one of the most horrific issues facing our nation today," said Interior Minister Wais Ahmad Barmak after Wednesday's attack on the Mawoud Academy, a private study institute in west Kabul.

Daesh claimed responsibility for the blast, which killed at least 34 people, most of them students attending an English class.

Most of the recent attacks on schools have been outside Kabul in provinces like Nangarhar, a stronghold of Daesh, whose tactics have become notorious since it first appeared in Afghanistan some four years ago.

The Taliban, at one time notorious for attacking schools and forcing girls and women to stay at home, now seek to influence schools by negotiation with local education officials and say they do not oppose schooling for girls. Its rival Daesh however, has stepped up its attacks on schools.UNICEF executive director Henrietta Fore said in a statement the agency was "gravely concerned" about the growing violence across Afghanistan. There is serious concern about more violence with the approach of parliamentary elections on Oct. 20, with 1,000 schools set to be used as polling stations, said UNICEF communication officer Alison Parker said. For children, the risk of violence has become a grim part of getting an education.