The attack came as Syrian security forces killed at least four people when they opened fire on thousands of demonstrators who took to the streets despite the near-certainty they will face gunfire, tear gas and stun guns.

Street battles have raged in Yemen's capital Sanaa for the last five days as tribesmen attempt to oust President Ali Abdullah Saleh.

At least 109 people have been killed by this week's street battles in Sanaa between security forces loyal to Saleh and fighters from Yemen's largest tribe, the Hashid, which has joined the popular uprising against the longtime ruler.

The fighting has hiked fears the country could be thrown into civil war as Saleh clings to power in the face of months of peaceful protests demanding his ouster.

Today's assault on the base in the el-Fardha Nehem region was the most significant escalation yet outside the capital.

Tribal fighters stormed the camp, 50 miles northeast of Sanaa, and killed dozens of troops - including the base commander - in the fighting, said Sheik Ali Saif, a leader from the Hashid tribe.

After the Hashid fighters captured the camp, government airplanes bombed them and other forces clashed with them on the ground, he said. At least 12 tribesmen were killed, Saif said. Read More