A suicide bomber has attacked an Afghan police convoy outside the capital Kabul, killing as many as 40 officers, officials say.Two bombs hit vehicles carrying cadets returning from a graduation ceremony on the city’s western outskirts.Paghman District Governor Haji Mohammad Musa Khan told the BBC many more had been injured.The bombing was claimed by the Taliban and follows an attack on a bus just over a week ago that killed 14 people.The dead included Nepali security guards working for the Canadian embassy.