Jan 18 (Reuters) - Syrian troops fighting U.S.-backed Kurdish-led forces seized the Omar oil field, the country’s largest, and the Conoco gas field in the eastern Deir Zor province as allied Arab tribal forces advanced in the oil-rich area along the border with Iraq, officials and security sources said on Sunday.

The takeover of the oil fields that lie east of the Euphrates River — a main source of revenue for the Kurdish-led forces — was a major blow to the group.