Yemen's government said 28 people were killed in an explosion at a weapons storage site Thursday, but the opposition claimed military forces shelled a building used by tribal fighters who have risen up against President Ali Abdullah Saleh and warn of civil war if he refuses to step down. The conflicting accounts, however, did not differ on the death count, which raised the overall toll to at least 109 since intense clashes broke out Monday in the heart of Yemen's capital and later spread to other areas of the city. The battles threaten to open a militia-led rebellion after months of street protests that have failed to end Saleh's 32-year rule. The escalating violence prompted the State Department on Wednesday to order nonessential U.S. diplomats and their families to leave the country. Yemen's Defense Ministry said the latest deaths occurred in an explosion at a weapons storage facility in a western part of Sanaa. The opposition, however, said shells slammed into a residential building occupied by fighters loyal to Sheik Sadeq al-Ahmar, the leader of the Yemen's largest and most powerful tribe.