Seven US soldiers working near a weapons cache were killed in an explosion west of the Afghan city of Ghazni, the Central Command announced. One US soldier was missing following the blast, Central Command said in a statement, adding that three US soldiers and an interpreter were injured. "The soldiers were working around a weapons cache when the explosion occurred. The wounded soldiers were evacuated to the 452nd Combat Support Hospital at Bagram Air Base, near Kabul," the statement said. It added that an investigation of the explosion had been opened. A US military spokesman in Kabul confirmed the details and said that the explosion occurred at about 3:00 pm (1230 GMT). "All I can add is that the wounded soldiers and interpreter are receiving the best medical care possible and we extend out condolences to the families of these brave warriors who were fighting for peace in Afghanistan," Lieutenant Colonel Bryan Hilferty said. The US embassy in Kabul could not immediately be reached for comment. The deaths bring to 107 the number of US soldiers killed while involved with Operation Enduring Freedom, although not all of those deaths were in Afghanistan. Ghazni is about 150 kilometres south west of Kabul, in the troubled southeast of the country. The south and southeast of Afghanistan have experienced an upsurge in violence in recent months, with aid workers and non-government organisations withdrawing most foreign staff from these areas. US troops are working in the Ghazni area to secure the newly-completed road linking the capital Kabul to the main southern city of Kandahar. They also plan to open a civil military reconstruction team in the area very soon. The news of the deaths follows two bombings in Kabul this week. The attacks killed three people and wounded more than a dozen others and were clearly targeting foreigners. The United States on Thursday warned US citizens in Afghanistan to stay off the streets of the capital, saying it was possible that such attacks might escalate in the coming days. The notice was released after a British peacekeeper was killed and four others wounded on Wednesday in the second car bomb attack in two days in Kabul. Officials said the bombing, carried out by a bomber who drove a yellow and white taxi into a two-vehicle British ISAF convoy as it was patrolling on the outskirts of Kabul quite close to the British base, was well-planned and indicated an upsurge of violence in the city. On Tuesday a bomber killed a Canadian ISAF soldier and an Afghan civilian and injured nine others when he walked up to a two-vehicle ISAF convoy and blew himself up. Taliban sources have claimed responsibility for the attacks and warned that more are to come. Two years after the ousting of the Islamic Taliban regime the US-led coalition of 12,000 troops comes under regular fire from Taliban remnants and their al-Qaeda allies.