US nuclear power giant Westinghouse Electric, a unit of Japan's Toshiba, said Friday it has extended its contract to supply fuel to Ukraine's nuclear power plants through 2020.

Westinghouse Electric said the contract, originally signed in 2008, was amended with the National Nuclear Energy Generating Company of Ukraine, known as Energoatom, the operator of the beleaguered country's four nuclear power plants.

"The contract provides for the continuation of the long-standing partnership between the two companies in providing competitive and secure nuclear fuel supplies for Ukraine's reactor fleet," Westinghouse Electric said in a statement.

The company did not provide details about the number of reactors to be supplied or the financial terms of the agreement.

Westinghouse will produce the fuel at its plant in Vasteras, Sweden.

The Pittsburgh, Pennsylvania-based Westinghouse's five-year contract to provide nuclear fuel supplies to three Ukrainian reactors was to expire in 2015.

Ukraine relies on nuclear power generation for nearly 50 percent of its energy requirements.

The contract extension comes amid the crisis over Ukraine, with Russia threatening to cut natural gas supplies to the country if it fails to pay a $2.2 billion debt.

The United States is working with Ukraine to provide financing and help it find enough natural gas.

On Thursday, US President Barack Obama threatened fresh sanctions against Moscow if it escalates the crisis. The US slapped sanctions on Russia following its annexation of Crimea, Ukraine's Black Sea peninsular region, last month.