Suicide bomber on donkey kills US troops The US army has suffered further casualties in Afghanistan. Kabul: Three US soldiers, four Afghan soldiers and an interpreter were killed on Tuesday morning in Wardak province after an insurgent riding a donkey detonated a bomb in one of the most hotly contested districts in the country, officials said. The attack occurred in the morning as the Americans and Afghans were conducting a joint patrol in a violent stretch of Sayadabad district, close to the main highway leading to Kabul. At least three more US soldiers were wounded in the bombing, for which the Taliban claimed responsibility. Although casualties among members of the international military coalition have decreased this year as the Afghans take the lead in fighting across the country, commanders have remained concerned about troop vulnerability as the fighting season and withdrawal operations have coincided. US soldiers on patrol in Afghanistan. Wardak in particular has been troubled this fighting season, as insurgents focus their energy on planning and executing attacks in neighboring Kabul. The province is a crucial channel to the capital for weapons and explosives smuggled by the Taliban. Aside from the violent environment, Wardak has also become a centre of political tension between the government and coalition forces operating in the area. After at least 17 Afghan villagers who had been detained by a US Special Forces unit in Nerkh district went missing and were later found dead, with evidence of torture, President Hamid Karzai temporarily banned such elite troops from operating in the province. US officials say they have conducted three investigations into the matter and have cleared their troops of responsibility in any torture or killing in Nerkh. But they have refused to offer further explanation of what might have happened to the dead men, even as local Afghan civilians have focused on the role of Afghan irregulars who often accompanied the Americans. The Afghan government, which has conducted its own investigation, has detained a former interpreter for the US team, Zakariah Kandahari, who is accused of participating in the torture and killings. Much like Nerkh, Sayadabad district is a highly contested area, fought over by government forces, the Taliban and sometimes other militants. It runs along the main highway southwest of Kabul, on a crucial transportation route that essentially circles the country. Last year, suicide attackers targeted a base in the area, killing at least a dozen Afghans and wounding nearly 60. A similar attack occurred near the base a year earlier. Violence across Afghanistan this month has abated to some degree because of Ramadan, when Muslims fast during the day. But military and police commanders are bracing for an increase in violence in August, when the fasting season ends.