Earlier, Turkey and the United Nations said the deal had been extended but did not say for how long. A Ukrainian government minister said it would last 120 days.

Foreign Ministry spokeswoman Maria Zakharova posted a copy of a letter from Russia's permanent representation to the United Nations saying Moscow would not object to the deal being extended by 60 days to May 18.

"Consideration by the Russian side of a further extension of the (deal) after the indicated date will only be possible subject to tangible progress" being made on the question of exporting Russian food and fertilizer, it said.

Russia says that although these exports have not been explicitly targeted by the West, sanctions on its payments, logistics and insurance industries are creating barriers.

(Reporting by Reuters; Editing by Mark Trevelyan, David Ljunggren and Chizu Nomiyama)