BELGRADE, Nov 16 (Reuters) - Serbia has seven days to

decide on steps to safeguard fuel supplies from the Serbian

refinery of Russian-owned NIS without

nationalisation, President Aleksandar Vucic said on Sunday.

Washington is seeking complete Russian divestment from NIS,

which operates Serbia's only refinery, and on Saturday gave the

company's owners three months to find a buyer.

Banks have frozen NIS transactions and officials project

that the Serbian refinery only has enough crude oil to operate

until November 25.

"The decision ... must be made over the next seven days; the

refinery must operate," Vucic said on Sunday during a government

session aired live on state television.

Vucic said that Serbia wants to avoid nationalising Russian

assets and is ready to make an above-market offer for the

company should Russian negotiations with unnamed Asian and

European partners fail.

Russia's Gazprom Neft and Gazprom hold a

combined controlling stake of 56% in NIS and have notified the

U.S. Treasury's Office of Foreign Assets Control (OFAC) of their

willingness to transfer control to a third party.

Finance Minister Sinisa Mali warned on Sunday that prolonged

sanctions on NIS could undermine Serbia's economic growth,

credit ratings and foreign investment.

Gazprom Neft controls 44.9% of NIS and Gazprom 11.3% while

Serbia owns 29.9%, with the rest held by small shareholders.