Tribesmen seized an oil ministry building in Yemen's eastern Hadramout province on Thursday and exchanged gunfire with a pro-government tribe seeking to regain control of the premises, tribal sources and ministry employees said.
The tribesmen were responding to the killing of a tribal leader earlier this month in fighting at an army checkpoint after his bodyguards refused to hand over their weapons to soldiers.
Yemen, one of the Arab world's poorest countries, is struggling to restore state authority after long-serving President Ali Abdullah Saleh was forced to step down in 2011.
The authorities face regular challenges from tribesmen who attack oil pipelines and power lines for reasons including demands for more employment and the release of jailed relatives.
Sources said the building was under the control of al-Kathiry tribe who had told the oil ministry workers to leave. Details of casualties were not immediately available.
The tribesmen's demands include the handing over of the soldiers who killed the leader, Said bin Habrish, full withdrawal of the army from Hadramout and more jobs for local people.
The tribal chief's death has led to protests and clashes with soldiers in Hadramout and other southern cities.
Clashes between the armed forces and tribesmen continued late on Thursday in the city of Shahr in Hadramout, which resulted in the death of two soldiers and one tribesman, local sources told Reuters.
At least four people, including two soldiers, were killed in attacks on army checkpoints near oilfields in Wadi Hadramout on Monday, according to local sources. Yemen's army responded by attacking posts of the armed tribesmen.
Tribesmen bombed Yemen's main oil pipeline late on Wednesday and repairs will take several days to complete so that pumping can resume, officials said.
The attack, in the Wadi Obaida area of the central oil-producing province of Maarib, halted flows from the Maarib fields to the Ras Isa oil terminal on the Red Sea, they said.
Yemen relies on crude exports to finance up to 70 percent of budget spending.