Three homicide car bombs exploded outside Somalia's government base of Baidoa, killing at least six people, including the drivers, and wounding four civilians, officials said Thursday. One of the bombers was a veiled woman.

The bombing took place at a government checkpoint, exploding as police tried to check them, Deputy Defense Minister Salad Ali Jelle told The Associated Press.

"The three drivers were killed on the spot and three others who were with them," the minister said by telephone. "We have captured three who were with them who have tried to flee. The dead include non-Somalis, they are Al Qaeda supporters."

A police officer, who spoke on condition of anonymity because he was not authorized to speak to the media, said one of the bombers in the car was a woman wearing a veil.

Four civilians were taken to a hospital in Baidoa, he said.

No one has claimed responsibility for the attack.

On Sept. 18, President Abdullahi Yusuf escaped unharmed when a suicide bombing struck his convoy in Baidoa, although 11 people were killed in the blast and a subsequent gunbattle, including Yusuf's younger brother.

The transitional government blamed that bombing on extremists within the Islamic movement. The group denied it, and no one has claimed responsibility.

Tensions are high in this Horn of Africa nation where the Islamic movement and the Ethiopian-backed transitional government are vying for control. Analysts fear a war could engulf the region.

The top U.S. diplomat for Africa, Jendayi Frazer, warned Wednesday that Al Qaeda militants are operating with "great comfort" in Somalia, providing training and assistance to a radical military element loyal to the Islamic group.

The Islamic Council has been gaining ground since seizing the capital, Mogadishu, in June. The United States accuses the group of sheltering suspects in the 1998 Al Qaeda bombings of U.S. embassies in Kenya and Tanzania, which it denies.

The Islamic group's often severe interpretation of Islam raises memories of Afghanistan's Taliban, which was ousted by a U.S.-led campaign for harboring Osama bin Laden and his Al Qaeda fighters.