BELGRADE, Aug 22 (Reuters) - Russian-owned Serbian oil

company NIS has asked the United States for a sixth

waiver from sanctions that could cut its crude supply, the

pro-government Tanjug news agensy said on Friday.

NIS, majority-owned by Russia's Gazprom Neft and

Gazprom, operates Serbia's only oil refinery in the

town of Pancevo, just outside the capital Belgrade.

The facility has an annual capacity of 4.8 million metric

tons and covers most of the Balkan country's needs.

The U.S. Treasury's Office of Foreign Assets Control placed

sanctions on Russia's oil sector on January 10, and gave Gazprom

Neft 45 days to exit ownership of NIS.

NIS has so far secured five waivers, with the latest one set

to expire on August 27.

Gazprom Neft owns 44.85% of NIS, while Gazprom has 11.3%.

The Serbian government owns 29.87%, with small shareholders

accounting for the rest.