ANKARA, Turkey (AP) — Turkish officials say a deal on a U.N. plan to unblock the exports of Ukrainian grain amid the war and to allow Russia to export grain and fertilizers will be signed Friday in Istanbul.

Turkish President Recep Tayyip Erdogan's office said that he, U.N. Secretary General Antonio Guterres and officials from Russia and Ukraine will oversee the signing ceremony. It did not provide further details.

“The grain export agreement, critically important for global food security, will be signed in Istanbul tomorrow under the auspices of President Erdoğan and U.N. Secretary General Mr. Guterres together with Ukrainian and Russian delegations,” Erdogan spokesman Ibrahim Kalin said in a tweet.

Guterres has been working on a plan that would enable Ukraine to export millions of tons of grain that have been stuck in its Black Sea ports — a move that could ease a global food crisis that has sent wheat and other grain prices soaring. At least 22 million tons of grain are stuck there due to the war.

Last week, the sides met in Istanbul, reaching a tentative agreement on the plan. It foresees joint controls of ships as they leave and arrive at Black Sea ports, and a mechanism to ensure the safety of the transfer routes, Turkish officials said.

A coordination center for the shipping of exports would be established in Istanbul and would include U.N., Turkish, Russian and Ukrainian officials.

U.N. deputy spokesman Farhan Haq said Guterres arrived Thursday in Istanbul, which means “we’re moving ahead” on the deal. U.N. humanitarian chief Martin Griffiths, whom Guterres put in charge of the Ukraine side of the deal, and Rebeca Grynspan, head of the U.N. Conference on Trade and Development, whom he put in charge of the Russian side, were also in Istanbul.

“We’ve been working around the clock with intense behind the scenes talks with countless moving parts,” Haq said.

With the growing global food crisis, Haq said if an agreement is reached “we can potentially save hundreds of thousands, potentially millions of people, from having food be priced out of their reach.”

Russian and Ukrainian officials have blamed each other for the blocked grain shipments.

Moscow accused Ukraine of failing to remove sea mines at the ports to allow safe shipping. Russia has also insisted on its right to check incoming ships for weapons.

Ukraine has sought international guarantees that the Kremlin wouldn’t use the safe corridors to attack the Black Sea port of Odesa. Ukrainian authorities have also accused Russia of stealing grain from its eastern regions to sell, and deliberately shelling Ukrainian fields to set them on fire.

On Thursday evening, a spokesman for Ukraine’s foreign ministry appeared to lay out Kyiv’s conditions for backing the plan.

Oleh Nikolenko told reporters that Ukraine's delegation "will support only those decisions that will guarantee the security of the southern regions of Ukraine, the strong position of the Armed Forces of Ukraine in the Black Sea and the safe export of Ukrainian agricultural products to world markets.”

The Kremlin's spokesman declined to comment on the Turkish announcement. Dmitry Peskov said it was a question “for the (Russian) military.”

In Washington, State Department spokesman Ned Price said the U.S. welcomes the agreement in principle. “But what we’re focusing on now is holding Russia accountable for implementing this agreement and for enabling Ukrainian grain to get to world markets. It has been for far too long that Russia has enacted this blockade,” Price said.

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