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BELGRADE, June 16 (Reuters) - Serbia's Russian-owned and U.S.-sanctioned NIS oil firm has secured a sanctions reprieve from the U.S. Treasury until July 1 that will allow it to continue importing and processing crude oil, state RTS TV reported on Tuesday, citing sources.

The U.S. Treasury's Office of Foreign Assets Control is also expected to grant an extension for Hungary's MOL to negotiate the purchase of the 51.56% stake in NIS owned by Russia's Gazprom Neft and Gazprom, Serbian President Aleksandar Vucic said earlier in the day.

The U.S. Treasury did not immediately respond to a request for comment.

OFAC imposed sanctions on NIS in October as part of targeting Russia's energy sector over the war in Ukraine and demanded Russian firms divest the shares they own in NIS.

The U.S. sanctions also forced NIS, which owns the only refinery in Serbia, to seek waivers from OFAC to buy and process crude oil, which it would not require once the share sale is completed.

MOL signed an agreement in January to buy the combined Gazprom Neft and Gazprom 51.56% stake, pending OFAC approval. Washington gave them until June 16 to complete the sale.

Vucic said in a live broadcast from the Georgian capital Tbilisi, where he is on a state visit, that he had been informed there would be a 15-day extension. He added he hoped the Russian side would accept the deal.

MOL, NIS and Gazprom Neft could not be immediately reached for comment.

Also on Tuesday, Serbia, which holds 29.9% of NIS, and MOL formally signed a shareholders' agreement over Belgrade's minority stake in the company, which is separate from acquisition talks between MOL and Russian companies.