An explosion rocked the headquarters of Guinea-Bissau's armed forces late Sunday, wounding at least three soldiers, witnesses said. It was not immediately clear what caused the blast. Defense Minister Artur Silva and other top officials contacted by The Associated Press declined to comment. In November, renegade soldiers attacked President Joao Bernardo Vieira's home with automatic weapons, killing at least one guard in a failed coup attempt that was repulsed by loyalist security forces. On Sunday in the capital, Bissau, troops closed roads around the armed forces building and prevented reporters from approaching. The British Broadcasting Corp. reported that the unexplained blast had destroyed part of the building. Soldiers also shut down the city's five private radio stations, said Zikue Swaeibi, a journalist at one of them, Radio Bombolom. Only state radio was on the air, but it played only traditional music and there were no news broadcasts. The three soldiers wounded in the blast were taken to the main public hospital, according to a source who visited the hospital. Two of the soldiers were covered in blood and a third suffered severe burns. Guinea-Bissau has had multiple coups and attempted coups since 1980, when Vieira himself first took power in one. The U.N. says the impoverished nation on the Atlantic coast of Africa has become a key transit point for cocaine smuggled from Latin America to Europe.