Yemen tribes kill six soldiers, tell Norway DNO to end oil work ADEN (Reuters) - Yemeni gunmen killed at least six soldiers in stepped up attacks on army installations in the southeastern Hadramout province, a local official and residents said on Sunday, after tribesmen warned Norway's DNO to stop operations in the area. Growing lawlessness in the poor Arabian Peninsula state is an international concern because of Yemen's strategic position next to oil exporter Saudi Arabia and shipping lanes. Armed tribesmen Hadramout have been targeting government troops and facilities in the area since early December, when a local tribal leader was killed in a gunfight at an army checkpoint after his bodyguards refused to hand over their weapons to soldiers. A local government official in al-Shihr said tribesmen tried to overrun an army camp on the outskirts of the Arabian Sea city on Sunday, killing four soldiers. Residents said mortars and rocket propelled grenades were heard across the city. The attack came hours after armed tribesmen attacked troops assigned to guard oil wells near a facility operated by DNO. "There was an attack yesterday on a military vehicle close to a military check point," DNO acting managing director Bjoern Dale told Reuters. The attack took place several kilometers south of our facility. DNO received a letter from the organization Hadramout Tribes Confederacy on Friday. The attack was one day after a tribal alliance in the area warned the company to suspend all its operations starting on Saturday, pending the government heeding demands to handover soldiers who killed Said bin Habrish, a prominent tribal chief, earlier in December. The local official said two soldiers were killed and one was injured in the attack. Local tribesmen confirmed the attack but said three soldiers died and six were injured. Bin Habrish's death has led to protests and attacks on government facilities, including a brief seizure of the Yemeni oil ministry offices in Hadramout, in which several people were killed. Apart from handing over of bin Habrish's killers, tribesmen also demanded full withdrawal of the army from Hadramout and more jobs for local people. Yemen, one of the poorest countries in the Arab world, has been in political turmoil since mass protests in 2011 forced long-serving President Ali Abdullah Saleh to step down under a Gulf initiative in which he was succeeded by deputy Abd-Rabbu Mansour Hadi. Alongside tribal lawlessness, Yemen also faces more attacks by al Qaeda, rising sectarian tensions in the north and a secessionist movement in the south. Yemen relies on crude exports to finance up to 70 percent of budget spending. Reporting by Mohammed Mukhashaf in Aden and Balazs Koranyi in Oslo,; Writing by Sami Aboudi, editing by William Hardy