SANAA (AFP) - At least 18 people have been killed and more than 40 others wounded in renewed clashes in Yemen's capital and its second city, medics and activists said on Wednesday, after a brief period of calm. Armed clashes broke out early Wednesday in the flashpoint city of Taez between government forces and tribesmen who support a mass protest movement calling for President Ali Abdullah Saleh's resignation, said activists. Eight civilians, including a 13-year-old boy, and two gunmen were killed and 43 people wounded, mostly civilians, in the ensuing violence, according to the latest toll provided by medical officials. The ministry of interior said five Yemeni soldiers were also killed in the clashes, accusing the opposition of targeting its troops. But residents and gunmen said pro-Saleh troops were targeting Taez neighbourhoods with heavy weapons, including mortar and tank shells, damaging some high-rise buildings. Witnesses said fires and smoke were seen rising from the city, where clashes continued into the afternoon with heavy shelling rocking central and northern Taez. In Sanaa, intermittent clashes erupted late Tuesday in Hasaba district between government troops and gunmen loyal to influential tribal chief Sheikh Sadeq al-Ahmar, killing two tribesmen and a policeman, said medical officials and the interior ministry. At least seven others were wounded in the restive district, the scene of fierce clashes and shelling in past weeks, said the medics. The violence comes after a brief lull in bloodshed as government troops battle a nine-month uprising by pro-democracy activists, dissident soldiers, and tribal gunmen against Saleh's 33-year-rule. International and regional mediators have failed to secure a Gulf-sponsored deal between Saleh and his opponents that would ensure a peaceful transition of power to the vice president until early elections for a new president. The deadlock has left Yemen's economy and government in turmoil, and triggered a wave of unrest costing hundreds of lives and injuring thousands more since the start of the anti-Saleh protest movement in January.