A car bomb exploded outside a United Nations office in this southern Afghan city Tuesday, wounding at least one person, a U.N. official said. Meanwhile, in a mountainous area of eastern Afghanistan, American and Afghan troops clashed with two groups of fighters, killing one and causing the others to retreat in to Pakistan, the U.S. military said. The explosion in Kandahar's upscale residential area of Shehr-e-Nau, occurred in a vehicle parked in front of a home being used as a workplace by the U.N. Office Project Support, said Siddiqullah, an Afghan who is in charge of humanitarian operations for the United Nations in southern Afghanistan. The blast, which occurred minutes after U.N. workers had left the building at the end of their work day, smashed a front gate, cracked walls in the building and broke its windows, said Siddiqullah. It also similarly damaged an adjacent building housing the U.N. Assistance Mission for Afghanistan, he said. There was no immediate claim of responsibility, but Gen. Mohammed Salim Khan, deputy chief of Kandahar police, blamed the Taliban and al-Qaida. Both offices will be closed Wednesday as U.N. officials review the situation. U.N. special envoy for Afghanistan, Lakhdar Brahimi, was to meet with senior U.N. officials in Kabul to decide if the southern area was too dangerous for its workers. In New York, U.N. spokesman Fred Eckhard insisted, "the United Nations is not relocating out of Kandahar, although staff movement within the city has been temporarily suspended." The world body has been forced to cut down its foreign staff in Iraq after a devastating car bomb attack against its headquarters in Baghdad. Kandahar is a former stronghold of the Taliban movement which ruled most of Afghanistan before it was driven out of power by a U.S.-led invasion and replaced by an Afghan government and warlords supported by the coalition. **PHOTO CAPTION*** Two unidentified men examine the remains of a vehicle following an explosion on Tuesday night, Nov.11, 2003 in Kandahar, southern Afghanistan. (AP Photo/Noor Khan)