Kyiv (Ukraine) (AFP) - Russian missiles hit Ukraine's port of Odessa Saturday, in what Kyiv called a "spit in the face" of a day-old deal between the warring sides to resume cereal exports blocked by the conflict.

The Ukrainian military said its air defences had shot down two cruise missiles but two more hit the port, threatening the landmark agreement hammered out over months of negotiations aimed at relieving a global food crisis.

The Ukrainian foreign ministry spokesman said the strike was "a spit in the face" by Russian leader Vladimir Putin against the deal brokered by Turkish President Recep Tayyip Erdogan and United Nations chief Antonio Guterres.

Guterres -- who presided over the signing ceremony on Friday -- "unequivocally" condemned the reported attack on Odessa, his deputy spokesman said, and urged all sides stick to the deal to allow grain exports.

"These products are desperately needed to address the global food crisis and ease the suffering of millions of people in need around the globe," he said.

The EU's foreign policy chief Josep Borrell directly blamed Russia for the strikes.

"Striking a target crucial for grain export a day after the signature of (the) Istanbul agreements is particularly reprehensible and again demonstrates Russia's total disregard for international law and commitments," he said.

20 million tonnes of wheat

There was no immediate reaction from Moscow after the attack.

Ukrainian foreign ministry spokesman Oleg Nikolenko said Russia would bear "full responsibility for deepening the global food crisis" if the assault jeopardised the agreement.

The first major accord between the countries since the February invasion of Ukraine aims to ease the "acute hunger" that the United Nations says faces an additional 47 million people because of the war.

Hostility between Moscow and Kyiv had spilled over into Friday's signing ceremony in Istanbul -- delayed briefly by disputes about the display of flags around the table and Ukraine's refusal to put its name on the same document as the Russians.

Ukraine had entered the ceremony by bluntly warning that it would conduct "an immediate military response" should Russia violate the agreement and attack its ships or stage an incursion around its ports.

The two sides eventually inked separate but identical agreements in the presence Guterres and Erdogan at Istanbul's lavish Dolmabahce Palace.

Guterres, moments before the signing, hailed the agreement as "a beacon of hope".

Ukrainian President Volodymyr Zelensky later said the responsibility for enforcing the deal would fall to the United Nations, which along with Turkey is a co-guarantor of the agreement.

The agreement includes points on running Ukrainian grain ships along safe corridors that avoid known mines in the Black Sea.

Thousands of people have been killed and millions displaced from their homes since Russia invaded its pro-Western neighbour on February 24.

Huge quantities of wheat and other grain have also been blocked in Ukrainian ports by Russian warships and landmines Kyiv has laid to avert a feared amphibious assault.

Zelensky said that around 20 million tonnes of produce from last year's harvest and the current crop would be exported under the agreement, estimating the value of Ukraine's grain stocks at around $10 billion.

Russian Defence Minister Sergei Shoigu told Kremlin state media he expected the deal to start working "in the next few days" although diplomats expect grain to only start fully flowing by mid-August.

The United States and Britain hailed the accord but urged Moscow to abide by its rules.

Strikes on central Ukraine

The ornate halls of Istanbul's Dolmabahce Palace felt far removed from east Ukraine's Donbas war zone on another day of relentless shelling across the front.

Russia is trying to fight deeper into the war zone's Donetsk region after securing full control of neighbouring Lugansk.

Russian missile strikes on railway infrastructure and a military airfield in the central area of Kirovograd on Saturday killed at least three people and wounded 16 more, regional governor Andriy Raikovych said.

At least one of the dead was a serviceman, he said earlier, in a rare admission of a military casualty in a conflict in which military deaths have been closely guarded by both sides.

On Friday, the United States signed off on another $270 million in military aid to Ukraine, including rocket systems, artillery ammunition and armoured command posts.

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