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At least six militants and two soldiers have been killed in Yemen in fighting near a damaged oil pipeline east of the capital Sanaa.
Separately, gunmen and bombers targeted three senior military officers and the transport minister in a series of attacks in the capital Sanaa.
In one incident, two gunmen riding a motorbike shot dead Brigadier Fadel Mohammed Ali, an adviser to the minister of defence, outside the ministry's offices in Sanaa, a police source said. Further details were not immediately available.
Gunmen fired at the home of Transport Minister Waed Batheeb, wounding two of his guards, a transport ministry official said. A colonel was seriously wounded in an attack by gunmen and another officer survived a thwarted bomb attack on his car.
The fighting in turbulent Maarib province broke out when government troops backed by air strikes tried to secure the pipeline and repair damage inflicted last month by local militants, the official said.
He added that the army controlled the area surrounding the pipeline after Tuesday's clashes.
Yemen's oil and gas pipelines have repeatedly been sabotaged by Islamist fighters or tribesmen since an uprising erupted last year, causing fuel shortages and slashing export earnings for the impoverished country.
Yemen's stability is a leading security goal for the United States and Gulf Arab allies because of its strategic position next to top oil exporter Saudi Arabia and shipping lanes, and because it is home to one of the most active wings of al Qaeda.
Under an agreement reached earlier this month between tribal chiefs and the government, tribes in Maarib were meant to stop militants from attacking the pipeline in return for a halt to air strikes in the area.
A local official said troops were deployed on Tuesday after tribesmen failed to secure the pipeline or to hand over fighters involved in the killings of 17 army officers and soldiers in an ambush earlier in December. They were killed while inspecting the pipeline.
The affiliation of the militants in Maarib is unclear. Local sources said some had links to al Qaeda, while others were involved in kidnapping foreigners to pressure the government to release jailed kinsmen.
Officer wounded in capital
Yemen-based Al Qaeda in the Arabian Peninsula has mounted operations in Saudi Arabia and attempted attacks against the United States, which has stepped up strikes by drones.
In the capital, the ministry of defence said one man was arrested on Tuesday for planting a bomb in the car of an officer at the Central Security Forces. The attempt to blow up the car was foiled, the ministry said. Colonel Sameer al-Gharbani, an officer in the Republican Guard, was critically wounded in an attack by unidentified gunmen, a source at the Guard said.
The string of attacks happened less than a week after President Abd-Rabbu Mansour Hadi overhauled the armed forces as part of a Gulf-brokered power-transfer plan that helped ease former President Ali Abdullah Saleh from power in February.