STORY: Ukraine says Russia is again blocking the U.N.-backed Black Sea grain deal.
Kyiv accused Moscow on Thursday (June 1) of halting the registration of ships to all Ukrainian ports.
A U.N spokesman said Russia told officials it would limit registrations to the port of Pivdennyi in Ukraine's Odesa province.
The U.N. and Turkey brokered the Black Sea Grain Initiative last July.
It is designed to tackle a global food crisis made worse by Russia's invasion of Ukraine, which is a leading grain exporter.
Russia agreed to a two-month extension of the deal in May.
But it now says it will halt the deal unless an agreement is fulfilled to overcome obstacles to exports of its own grain and fertilizer.
The U.N. said there had been a "continuous slowdown" in vessel departures from April through May.
It also said the average daily inspection rate for ships had fallen to three.
The Ukrainian ministry claimed Russia had registered only one incoming ship for inspection in the last two days of May.
It called that a "gross violation" of the initiative.
Russia did not immediately comment on the ministry's statement.
Kyiv said 50 vessels were waiting for inspection in Turkish waters, ready to deliver 2.4 million tonnes of Ukrainian food abroad.
Some vessels had waited for inspections for more than 3 months.