Ukraine pressed ahead on Sunday with efforts to restart grain exports from Odessa and other Black Sea ports despite a missile attack that came a day after a Turkey-brokered deal aimed at easing global food shortages caused by the war was sealed in Istanbul.

Ukrainian President Volodymyr Zelenskyy denounced the strikes on Odessa as blatant "barbarism" that showed Moscow could not be trusted to implement Friday's deal, mediated by Turkey and the United Nations.

However, a government minister said preparations to resume grain shipments were ongoing. Public broadcaster Suspilne quoted the Ukrainian military as saying the missiles had not significantly damaged the port.

Russia said on Sunday its forces had hit a Ukrainian military boat in Odessa with missiles.

The deal signed by Moscow and Kyiv was hailed as a diplomatic breakthrough that would help curb soaring global food prices.

On Saturday, wheat prices tumbled back to levels last seen before Moscow invaded its neighbor.

In Chicago, the price of wheat for delivery in September dropped 5.9% to $7.59 per bushel, which is equivalent to about 27 kilograms (60 pounds) and the lowest close since Russia invaded Ukraine on Feb. 24. On Euronext, wheat prices for delivery in September fell 6.4% to $325.75 per ton.

Russia and Ukraine together produce about 30% of the world's wheat exports. Up to 25 million tons of wheat and other grain have been blocked in Ukrainian ports by Russian warships and land mines Kyiv has laid to avert a feared amphibious assault.

Despite Friday's retreat in wheat prices, analysts expressed skepticism about the accord's ability to sidestep the realities of the grinding Russia-Ukraine conflict amid doubts over Moscow's willingness to implement the deal.

While the main theater of combat has been the eastern region of Donbass, Zelenskyy said in a video posted late on Saturday that Ukrainian forces were moving "step by step" into the occupied eastern Black Sea region of Kherson.

Ukraine's military on Sunday reported Russian shelling in numerous locations in the north, south and east, and again referred to Russian operations paving the way for an assault on Bakhmut in Donbass.

The country's air force command said that it had shot down three Kalibr cruise missiles launched on Sunday morning by the Russian forces from the Black Sea and aimed at the western Khmelnytskyi region.

The strikes on Odessa drew condemnation from the United Nations, the European Union, the United States, Britain, Germany and Italy. On Friday, United Nations officials had said they hoped the agreement would be operational in a few weeks.

Video released by the Ukrainian military showed firefighters battling a blaze on an unidentified boat moored alongside a tug boat. Reuters was unable to independently verify the authenticity of the video or the date it was filmed.

The Russians told us that they had absolutely nothing to do with this attack and they were looking into the issue very closely," Turkish Defense Minister Hulusi Akar said Saturday.

"The fact that an incident like this happened after the agreement we made yesterday ... really makes us concerned," he said.

On Sunday, though, Russian Foreign Ministry spokesperson Maria Zakharova said that Russian forces had hit a Ukrainian military boat in of Odessa with high-precision missiles.

According to the Ukrainian military, two Russian Kalibr missiles hit the area of a pumping station at the port and two others were shot down by air defense forces.

Ukrainian air force spokesperson Yuriy Ignat said the missiles were fired from warships in the Black Sea near Crimea.

Suspilne quoted Ukraine's southern military command as saying the port's grain storage area was not hit.

"Unfortunately, there are wounded. The port's infrastructure was damaged," said Odessa region governor Maksym Marchenko.

But Infrastructure Minister Oleksandr Kubrakov said on Facebook that "we continue technical preparations for the launch of exports of agricultural products from our ports."

Ukraine could export 60 million tons of grain in eight to nine months if its ports were not blockaded, but Russia's strike on the port of Odessa showed it will definitely not be that easy, an economic adviser to the Ukrainian president separately said Sunday.

Ukraine could earn $10 billion by selling 20 million tons of grain in silos and 40 million tons from its new harvest, adviser Oleh Ustenko said. The harvest totals 60 million tons, of which 20 million are for domestic consumption, he said.

"If the ports were unblocked now and we say we need to move 60 million tons of grain ... then we would transport 60 million tons of grain within eight-nine months," he said.

"But with the way they are opening now and what Russia is doing in the Black Sea, yesterday's strike shows that it definitely won't work that way," he said.

Ukraine will need 20 to 24 months to export those volumes if its ports are not functioning properly, he said.

The deal would restore grain shipments from the three reopened ports to prewar levels of 5 million tons a month, U.N. officials said.

During a Friday signing ceremony in Istanbul, U.N. Secretary-General Antonio Guterres hailed the deals to open Ukraine's ports in Odessa, Chornomorsk and Yuzhny to commercial food exports as "a beacon of hope, a beacon of possibility, a beacon of relief in a world that needs it more than ever."

Safe passage

The strikes appeared to violate Friday's deal, which would allow safe passage in and out of Ukrainian ports.

Zelenskyy vowed to do everything possible to acquire air defense systems able to shoot down missiles like those that hit Odessa.

The blockade of Ukrainian ports by Russia's Black Sea fleet has worsened global supply chain bottlenecks. Along with Western sanctions on Russia, it has stoked food and energy price inflation. Russia and Ukraine are major global wheat suppliers, and a global food crisis has pushed some 47 million people into "acute hunger," according to the World Food Programme.

Moscow denies responsibility for the food crisis, blaming Western sanctions for slowing its food and fertilizer exports and Ukraine for mining the approaches to its ports.

U.S. Secretary of State Antony Blinken said in a statement that the attack on Odessa "casts serious doubt on the credibility of Russia’s commitment to yesterday’s deal."

Guterres condemned the strikes and said full implementation of the deal was imperative.

Ukraine has mined waters near its ports as part of its war defenses, but under the deal, pilots will guide ships along safe channels.

A Joint Coordination Center staffed by members of the four parties to the agreement is to monitor ships passing through the Black Sea to Turkey's Bosporus and off to world markets. All sides agreed on Friday there would be no attacks on these entities.

Putin calls the war a "special military operation" aimed at demilitarizing Ukraine and rooting out dangerous nationalists. Kyiv and the West call this a baseless pretext for an aggressive land grab.