SANAA, Yemen - Yemeni officials say 18 people have been killed and at least 30 wounded in clashes between regime forces and its rivals.

The officials said eight followers of a tribal leader who defected to the opposition in March were killed early Monday in clashes with forces loyal to President Ali Abdullah Saleh in the Yemeni capital, Sanaa.

They said four civilians were killed in the fighting along with two government troops.

Three people were also killed when mortars exploded in a protest encampment in central Sanaa.

Also, a man was killed in the city of Taiz, when pro-government gunmen fired on protesters.

At least 30 were wounded across Sanaa and in Taiz.