Kabul — An attacker dressed in a school uniform set off a grenade amid a group of hundreds of university students in Afghanistan's capital on Sunday, killing himself and wounding five students, according to the district police chief.Nasir Nadery said the attacker, who slipped past two guards, was wearing an explosives vest that failed to explode. The students were inside a private compound where they were taking classes to prepare for university exams.The attack took place in a Kabul neighborhood dominated by ethnic Hazaras, a Shi’ite minority frequently targeted by the Sunni extremists. No one immediately claimed the attack, which resembled previous assaults carried out by the Islamic State group.On Saturday, a sticky bomb attached to the motorcycle driven by a retired Pakistani army officer exploded in southern Zabul province's Shahjoy district, killing the officer and his guard, according to the provincial government spokesperson, Gul Islam Seyal.Pakistan has been criticised by both the United States and Afghanistan for aiding Taliban insurgents, a charge it denies. Seyal said the retired officer was aiding the Taliban, although he did not provide any proof of his claim.A Pakistani military official said they have no knowledge of any retired officer killed in Afghanistan. He spoke on condition of anonymity in line with regulations.Meanwhile Taliban attacked security positions northwest of Kabul, killing at least five police and setting off a two-hour gunbattle, according to Mohammed Zaman, the police chief for Ghazni province.The Taliban have stepped up attacks across Afghanistan since the US and NATO formally concluded their combat mission at the end of 2014.In the western Ghor province, meanwhile, a roadside bomb killed a young shepherd and wounded five others. Police spokesperson Iqbal Nizami said the Taliban planted the bomb in order to target security forces.In the eastern Khost province, police spokesperson Basir Bina said a roadside bomb killed two children and wounded another nine. Both bombs went off on Saturday.