An explosion outside a school in Afghanistan has killed at least 25 people, including 15 students.The blast in Logar province is the bloodiest single attack in a year and the latest incident in a rising spiral of violence across the country. The device went off early on Thursday morning as police checked a vehicle abandoned between two schools. Officials say the explosives were hidden beneath a pile of firewood in the back of he truck which had crashed overnight, sparking speculation they were meant for elsewhere – possibly an attack in Kabul. The Taliban have been active for some time in Logar province, which lies close to the militant group’s eastern strongholds. Last week, US Marines lauched Operation Strike of the Sword – the first major operation under Barack Obama’s new strategy to defeat the Taliban and stabilise the country. At least 17 foreign soldiers, including seven Britons, have also been killed in the past six days, making it one of the bloodiest weeks for allied forces in many months.