A deal on a United Nations plan to unblock the export of Ukrainian grain and to allow Russia to export grain and fertiliser will be signed on Friday in Istanbul, Turkish officials said.

President Recep Tayyip Erdogan’s office said that he, UN Secretary General Antonio Guterres and officials from Russia and Ukraine will oversee the signing ceremony.

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

Last week, the sides met in Istanbul, reaching tentative agreement on the proposals.

The plan 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 centre for the shipping of exports would be established in Istanbul and would include UN, Turkish, Russian and Ukrainian officials.

“The grain export agreement, critically important for global food security, will be signed in Istanbul tomorrow under the auspices of President Erdogan and UN Secretary General Mr Guterres together with Ukranian and Russian delegations,” Mr Erdogan’s spokesman Ibrahim Kalin said.

At least 22 million tons of grain are stuck in Ukraine due to the war.

UN deputy spokesman Farhan Haq said the fact that Mr Guterres was traveling to Istanbul means “we’re moving ahead” on the deal.

UN humanitarian chief Martin Griffiths, whom Mr Guterres put in charge of the Ukraine side of the deal, and Rebeca Grynspan, head of the UN Conference on Trade and Development, in charge of the Russian side of the deal, were already in Istanbul.

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

With the growing global food crisis, Mr 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 the incoming ships for weapons.

Ukraine has sought international guarantees that the Kremlin would not use the safe corridors for grain shipments to attack Ukraine’s key 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.