Russia is not preparing to attack civilian ships in the Black Sea despite assertions by the United States, Russia's ambassador to Washington said on Thursday, in comments posted by his embassy.

On Wednesday, Moscow said it would deem all ships travelling to Ukrainian ports to be potential carriers of military cargo and their flag countries to be parties to the conflict on the Ukrainian side, after Russia quit a year-old deal to give ships exporting Ukrainian grain safe passage despite the war.

Commenting on the decision, the White House said Russia could expand its attacks on Ukrainian grain facilities to include attacks on civilian shipping in the Black Sea.

Ambassador Anatoly Antonov said in comments posted on the embassy's Telegram account: "Attempts to attribute to Russia the preparation of some attacks on civilian ships are pure falsification ...

"We regard the U.S. statements as an attempt to disguise by any means its own destructive activities, aimed at the de facto sabotage of the implementation of the interrelated Istanbul agreements."

Moscow on Monday quit the deal under which it had allowed Ukraine to export grain from its Black Sea ports to alleviate a global food crisis.

Russia said a parallel memorandum signed in Istanbul at the same time had been ignored. That was intended to facilitate Moscow's own grain and fertiliser exports in the face of Western sanctions on Russia in response to its invasion of Ukraine.

(Reporting by Reuters; Editing by Kevin Liffey and Cynthia Osterman)