The Black Sea grain deal was agreed to help tackle a global food crisis aggravated by Moscow's invasion of Ukraine in February 2022.
Under the agreement, all ships bound for Ukrainian ports must be inspected by a joint team including Russian inspectors. The Russian inspectors have since Apr 29 refused to inspect ships bound for Pivdennyi, Vaskov said.
Pivdennyi is the largest port included in the deal in terms of throughput. Restoration ministry data show it is storing about 1.5 million tonnes of food items for future export to 10 countries, with 26 ships due to come for them.
US State Department spokesperson Matthew Miller told reporters on Tuesday that Russia's actions were "a clear violation of their commitments" under the grain deal.
"(Russia's) continued obstruction of this initiative and threats to withdraw threaten to push up global food prices, threaten to reduce food accessibility for vulnerable populations around the world, and we once again call on Russia to stop holding global food supplies hostage," Miller said.
The Russian embassy in Washington did not immediately respond to a request for comment on Miller's remarks.
DEAL 'NOT WORKING AS IT SHOULD'
Vaskov said that Tuesday's inspections plan showed Russia had included only three of the 13 ships that had been submitted. All ships bound for Pivdennyi had been excluded, he said, as well as some meant to go to Odesa and Chornomorsk.
Russia's team had inspected only nine ships in all from May 19 to May 21, Ukrainian officials said.
"The grain initiative has been formally unblocked (extended), but it is not working as it should. Russia continues to slow it down as much as possible," he said.
Vaskov told Reuters last week that 62 vessels were ready for inspection and some of them had been standing by for several months. Russia has denied slowing inspections.
Moscow initially opposed extending the grain export deal unless demands regarding its own agricultural exports were met.
While Russian exports of food and fertiliser are not subject to Western sanctions, Moscow says restrictions on payments, logistics and insurance have amounted to a barrier to shipments.
Before it invaded Ukraine in February last year, Russia used Pivdennyi to send up to 2.5 million tonnes of ammonia abroad annually that arrived at the port after shipment via a pipeline from Togliati.
Uralchem, Russia's biggest potash and ammonium nitrate producer, expects the opening of an ammonia export terminal near the Black Sea to make a pipeline across Ukraine much less important, the company's CEO said.
According to the Joint Coordination Centre, which implements the Black Sea export deal, more than 30 million tonnes of food products have been exported from Ukrainian ports via the grain corridor so far, and just over 50 per cent of that was corn.