Yemeni tribesmen shot down an army helicopter killing eight soldiers, on Tuesday, during a clash over repairs to a main oil pipeline blown up by saboteurs, a tribal chief said. The armed tribesmen clashed with troops in Wadi Abida, in the lawless eastern province of Marib, as gunmen prevented maintenance teams from fixing the export pipeline blown up last week, the chief told AFP. Among the eight killed on the helicopter was Brigadier General Hussein al-Mashaba, head of Yemen\'s force tasked with protecting oil installations, the source said. He said the gunmen shot down the chopper with a rocket. Yemeni tribesmen blew up the pipeline linking eastern oilfields to the Red Sea coast, halting the flow of oil, state media reported on Sunday. An official said at the time it was the \"second act of sabotage by the same group in 10 days.\" The attack interrupted the flow of oil along the 320 kilometre (200 mile) pipeline which links the Safer oilfields to the export terminal in Hodeida province on the coast. In December, the army launched an offensive against tribesmen suspected of being behind such attacks, sparking clashes that left 17 people dead. Impoverished Yemen produces about 300,000 barrels of oil per day, most of it for export. According to official figures, lost production due to pipeline attacks in the east cost the government more than $1 billion in 2012, while oil exports fell by 4.5 percent.