A senior U.S. official on Thursday urged the Central Asian resource-rich state of Turkmenistan to diversify its natural gas export routes.

Ex-Soviet Turkmenistan, which sells most of its gas to Russia, is currently building a pipeline to China.

The West is lobbying for another route, the Nabucco pipeline, that would deliver 30 billion cubic metres of Caspian Sea gas per year to Europe, bypassing Russia and instead going through the Caucasus.

"Time shows that this proposal is viable," Deputy Assistant Secretary of State George Krol told reporters.

Krol met Turkmen President Kurbanguly Berdymukhamedov earlier on Thursday. Besides Nabucco, they discussed U.S. participation in developing Turkmenistan''s gas reserves.

"This requires a lot of investment and technologies," Krol said.

Washington has stepped up its advocacy of the Nabucco pipeline since the war between Georgia and Russia in early August.

U.S. Vice President Dick Cheney, on a tour of U.S. allies in the Caucasus region that started in ex-Soviet Azerbaijan, stopped in Georgia and continued in Ukraine late on Thursday, pushed for Nabucco and other U.S.-backed energy plans.

The United States and the European Union want Nabuccco as a alternative to the Nord and South Stream pipelines that will be part-operated by Russian gas export monopoly Gazprom and will pipe Russian gas to western Europe.