The United Nations Thursday warned of a fresh risk to global food security, saying Russia is limiting the number of vessels permitted to collect Ukrainian grain from Black Sea ports.

The disruption is said to be a part of Russia's strategy to compel Kyiv to open a key pipeline for transporting a crucial fertilizer ingredient to international markets.

U.N. spokesperson Stephane Dujarric expressed serious concern that only 33 ships departed from Ukrainian ports in May, half the number compared to April, and exports of grain and other foodstuffs totaled just 1.3 million metric tons last month, less than half the amount of the previous month.

He said Russia informed the center in Istanbul coordinating the arrivals, departures and inspections of ships involved in the Black Sea Grain Initiative "of its decision to limit registrations in the port of Yuzhny as long as ammonia is not exported, and currently it’s not."

Ammonia is a key ingredient for fertilizer and Moscow wants Ukraine to open a pipeline from the Russian city of Togliatti to the Ukrainian port of Odesa which it used before the war to ship ammonia to its global customers.

Türkiye and the U.N. brokered the breakthrough initiative with Russia and Ukraine last July, opening a path for Ukrainian grain exports from three of its key Black Sea ports: Odesa, Chernomorsk and Yuzhny.

In a separate memorandum, the United Nations said it would work to overcome obstacles to Russian food and fertilizer shipments, which U.N. trade chief Rebeca Grynspan has been trying to do for months but Moscow has criticized the lack of results.

Ukraine's Ministry of Renovation and Infrastructure on Thursday said the grain deal had been halted again because Russia had blocked the registration of ships to all Ukrainian ports.

"The Joint Coordination Centre in Istanbul (which oversees the initiative) has announced that it is impossible to draw up an inspection plan for June 1 because of another unjustified refusal of the Russian delegation to register the incoming fleet for participation in the Initiative," the Ukrainian ministry said on Facebook.

To reinforce the failure to export its fertilizer, Russia in March unilaterally decided to renew the grain deal for 60 days instead of the 120 days outlined in the agreement. And just before its expiration, in another example of Moscow’s brinkmanship, it agreed on May 17 to another two-month extension until July 17.

Following Russia’s Feb. 24, 2022 invasion of Ukraine, one of the world’s major breadbasket, global food prices skyrocketed, hitting poorer, developing countries especially hard.

After the July agreements, food prices started to drop but Dujarric warned that "global hunger hotspots are increasing and the specter of food inflation and market volatility lurks in all countries."

Ukraine’s President Volodymyr Zelenskyy tweeted Wednesday that the port of Yuzhny is blocked and over 1.5 million tons of agricultural products are waiting there for shipment to at least 10 countries including Türkiye, China, Egypt and Bangladesh.

He urged everyone to pressure Russia to unblock food supplies saying, "Obviously the less food is supplied to these countries, to these regions, the higher the food prices are, the more people in these countries lose from their family budgets."

Dujarric noted that in May only three ships departed from the port of Yuzhny.

He said that since May 24 the number of teams inspecting ships has been reduced from three to two. This, along with the slowdown in registering ships, is creating a serious situation.

Ukraine called the move a "gross violation" of the initiative.

The U.N. has put forward practical suggestions "at the strategic and operational level" and will continue to engage with Russia and Ukraine, Dujarric said.

"In particular, we are looking for commitments on unconditional access of vessels to all three ports under the initiative, increased number of successful inspections completed per day and predictable registrations to avoid undue delay of vessels, exports of fertilizers, including ammonia, and the resumption of the Togliatti-Odesa ammonia pipeline," Dujarric said.