Russia and Ukraine will sign a deal on Friday to reopen Ukrainian Black Sea ports for grain exports, reported Reuters, raising hopes that an international food crisis aggravated by the Russian invasion can be eased.

Russia and Ukraine, both among the world's biggest exporters of food, will send their infrastructure and defence ministers respectively to a 1330 GMT signing ceremony in Istanbul, three sources told Reuters.

The Kremlin confirmed Defence Minister Sergei Shoigu would sign the Turkish and UN-brokered accord, hours after Ukrainian President Volodomyr Zelenskiy said he expected his country's seaports would soon be unblocked.

UN Secretary-General Antonio Guterres and Turkish President Tayyip Erdogan were to attend the ceremony.

The blockade by Russia's Black Sea fleet has worsened global supply chain disruptions and, along with Western sanctions imposed on Moscow, stoked high inflation in food and energy prices since Russian forces swept into Ukraine on 24 February.

Full details of the accord were not immediately released. But Russian state news agency TASS, citing an unnamed source, said that three Ukrainian ports including the biggest export hub Odessa would be reopened.

Some 20 million tonnes of grain are stuck in silos at Odessa, and dozens of ships have been stranded by Moscow's offensive.

Turkish Foreign Minister Mevlut Cavusoglu tweeted on Thursday that Friday's gathering in Istanbul would mark "the first step to solve the current food crisis".

The United States welcomed the deal and said it was focussing on holding Russia accountable for implementing it.

'PACKAGE' DEAL

Moscow has denied responsibility for the worsening food crisis, blaming instead a chilling effect from Western sanctions for slowing its own food and fertiliser exports and Ukraine for mining the approaches to its Black Sea ports.

The United Nations and Turkey have been working for two months to broker what Guterres called a "package" deal - to restore Ukraine's Black Sea grain exports while easing Russian grain and fertiliser shipments.

Russian Foreign Ministry spokesperson Maria Zakharova said the European Union had proposed relaxing some earlier sanctions to shore up global food security. Moscow hoped this would create conditions for unhindered exports of grain and fertilisers.

Diplomats said last week details of the plan included Ukrainian vessels guiding grain ships through mined port waters, with Turkey overseeing inspections of ships to allay Russian concerns they might smuggle weapons to Ukraine.

Turkey, a NATO member that has good relations with Russia and Ukraine alike, controls the straits leading into the Black Sea and has acted as a mediator on the grain issue.