By Pavel Polityuk

KYIV (Reuters) -Ukraine accused Russia on Tuesday of effectively cutting the Ukrainian port of Pivdennyi out of a deal allowing safe Black Sea grain exports as Russia complained that it had been unable to export ammonia via a pipeline to Pivdennyi under the pact.

The Black Sea deal - brokered last July by the United Nations and Turkey and extended last week for two months - covers the wartime export of food and fertiliser from the Ukrainian ports of Odesa, Chornomorsk and Pivdennyi.

The U.N. expressed concern on Monday that Pivdennyi had not received any ships since May 2 under the deal.

Ukrainian Deputy Renovation Minister Yuriy Vaskov accused Russia of a "gross violation" of the agreement. All ships are inspected by a joint team of Russian, Ukrainian, Turkish and U.N. inspectors, but Vaskov said the Russian inspectors had refused to inspect ships bound for Pivdennyi since April 29.

"They (Russia) have now found an effective way to significantly reduce (Ukrainian) grain exports by excluding the port of Pivdennyi, which handles large tonnage vessels, from the initiative," Vaskov said in written comments on Tuesday.

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.

U.S. State Department spokesperson Matthew Miller told reporters on Tuesday that Russia's actions were "a clear violation of their commitments" under the grain deal, calling on Moscow to "stop holding global food supplies hostage."

The Russian embassy in Washington did not immediately respond to a request for comment on Miller's remarks.

AMMONIA

The Black Sea grain deal was agreed to help tackle a global food crisis aggravated by Moscow's invasion of Ukraine in February 2022. The pact also covers ammonia, which Russia transported to Pivdennyi via pipeline for export before the war.

Russia had threatened not to renew the Black Sea deal unless a list of demands related to its own food and fertiliser exports was met. Restarting the ammonia pipeline is one of those demands, which the United Nations has been trying to broker.

Russia used to pump up to 2.5 million tonnes of ammonia annually for export via the pipeline from Togliati. Russia's U.N. Ambassador Vassily Nebenzia on Tuesday said that amount of ammonia could "produce 7 million tonnes of fertilisers."

"This amount of fertiliser would allow to produce enough food to supply to 200 million people. These deliveries should have started at the same time as those of Ukrainian food. However this never happened," he told the U.N. Security Council.

"The deficit of ammonia on the world markets stands at 70% due to the shortfall in volumes," Nebenzia said.

A Ukrainian government source told Reuters on Friday Kyiv would consider allowing Russian ammonia to transit its territory for export if the Black Sea grain deal was expanded to include more Ukrainian ports and a wider range of commodities.

Uralchem, Russia's biggest potash and ammonium nitrate producer, expects the opening of an ammonia export terminal near the Black Sea to make the pipeline across Ukraine much less important, the company's CEO said.

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.

Ukraine accused Moscow of slowing ship inspections under the Black Sea deal, which Russia denies.

"It is not working as it should. Russia continues to slow it down as much as possible," Vaskov said.

According to U.N. data, more than 30 million tonnes of food products have been exported so far under the Black Sea deal.