Ukraine said on Wednesday it was establishing a temporary shipping route via Romania, one of the neighbouring Black Sea countries.
Russia's Defence Ministry said flag states of ships travelling to Ukrainian ports would be considered parties to the conflict on the Ukrainian side from midnight Moscow time (2100 GMT on Wednesday).
U.S. officials have information indicating Russia laid additional sea mines in the approaches to Ukrainian ports, said White House National Security Council spokesperson Adam Hodge.
"We believe that this is a coordinated effort to justify any attacks against civilian ships in the Black Sea and lay blame on Ukraine for these attacks," he said.
Russian President Vladimir Putin accused Western countries of "perverting" the U.N.-backed deal formally called the Black Sea Grain Initiative.
Persons:
West, Vasyl Shkurakov, Volodymyr Zelenskiy, Adam Hodge, Vladimir Putin, Putin, Valery Shershen, Grant McCool, Stephen Coates
Organizations:
Ukrainian Coast Guard, Operational Command, Putin, International Shipping Organization, United, Sunday, Russia's Defence Ministry, White, National Security, Monetary Fund, Russian, Reuters, Pentagon, Ukraine, European Union, Thomson
Locations:
Izmail, Odesa, Ukraine, Moscow, Russia, Romania, United Nations, Turkey, Ukrainian, Russian, Africa, Asia, China, Azov, Crimea, Washington, Brussels, European