Clashes between Yemeni soldiers and armed tribesmen in the restive southern city of Taiz left 13 dead on Thursday, the Defense Ministry and a security official said.
A hotbed of opposition to the government and Yemen's second-largest city, Taiz has been regularly shelled by the military responding to hit-and-run attacks by tribesmen, and the latest bout has been going on since Tuesday.
The fighting has raged despite longtime President Ali Abdullah Saleh's agreement to step down.
Saleh has been the target of months of protests in a nationwide uprising inspired by other Arab Spring revolts, and some units of his military have switched sides and joined protesters demanding his ouster,
Saleh signed a U.S.-backed power transfer deal, brokered by neighboring countries, last week in the Saudi capital, Riyadh, to resolve his country's spiraling crisis. It transfers power to his vice president and grants Saleh immunity from prosecution
A statement from the Defense Ministry said five soldiers were among those killed on Thursday, while 15 soldiers were also wounded.
A Yemeni security official said four tribesmen and four civilians were also killed, and 28 people were wounded, mostly in shelling by government troops. The official spoke on condition of anonymity in line with security regulations.
The official also said that earlier in the day, tens of thousands of protesters had taken to Taiz streets to denounce the military's actions. He said some of the protesters also attacked houses belonging to members of Saleh's ruling party.
The official added that the military sent in reinforcements to Taiz outskirts, boosted troop positions on the hills and mountains surrounding the city and is preventing anyone from entering it.
A Taiz resident, Mohammed Abdul-Ghani, told The Associated Press over the telephone that demonstrators set fire to two of the military's armored cars and damaged several others, and also hurled rocks at the security forces. He said smoke from burning tires filled the air.
Abdul-Ghani said several shells fell near his street and he could see fires rising from where they hit. He said many residents were continuing to flee the city to rural areas.