(Bloomberg) -- Ukraine kicked off a long-awaited thrust in its counteroffensive with an armored assault on Russian fortifications in the south that may be part of a push to cut Moscow’s land link to its strongholds in occupied Crimea. 

The assault coincided with new Russian missile attacks against infrastructure in Ukraine’s Odesa region which killed one person and damaged a grain cargo. Wheat prices rose, continuing a climb that began last week when Ukraine’s Black Sea export deal collapsed.

A US official who asked not to be identified discussing details of military operations said Ukrainian troops were making a significant push in the southeastern Zaporizhzhia region. Russian officials also reported a major Ukrainian assault more than seven weeks after Kyiv launched attacks against invading forces across the frontline.

“Glory to all who defend Ukraine! By the way, our boys at the front had very good results today,” Ukrainian President Volodymyr Zelenskiy said in his evening address on Wednesday, without elaborating. “Well done! Details later.”

Analysts with the Institute for the Study of War said overnight that “a significant mechanized counteroffensive operation” appeared “to have broken through certain pre-prepared Russian defensive positions.” A wide range of diverging claims from Russian military bloggers on the scale of the attack and Ukrainian losses had made the situation unclear, they added.

The thrust comes as Russian President Vladimir Putin hosts a summit of African leaders in St. Petersburg. Intended to demonstrate Moscow’s growing influence in the Global South, the conference instead highlighted the Kremlin’s diminishing power because of the war. Only 17 heads of state were scheduled to attend, compared with 43 in 2019.

Read More: Putin Hosts Africa Summit in the Shadow of Grain Deal’s Collapse

Ukrainian officials have admitted in recent weeks that the counteroffensive has been more difficult than expected as their forces make slow progress fighting through Russian minefields, tank barriers and other defenses without being able to provide air support. 

At the same time, Kyiv and western military officials have pointed to a strategy of wearing down undermanned Russian units across the 1,500 kilometer (932-mile) front. 

The approach includes holding back the main assault force — including units trained by NATO member states and equipped with top-shelf weapons from the alliance — so that it can exploit weak spots and break through Russian lines. In the past Ukraine has also employed feints to disguise the main thrust of an attack, as when it attacked in the south before achieving a major breakthrough and retaking territory in the north of the country last fall.  

“The question on the table now is whether the Ukrainians are deploying some of the units that they’ve held back and putting all of those into the counteroffensive,” US Secretary of State Antony Blinken told reporters in Wellington, New Zealand.

Earlier, the New York Times cited two Pentagon officials it didn’t identify as saying Ukraine has launched the main thrust of its counteroffensive. A Ukraine embassy official, who also asked not to be identified, warned against framing any part of the counteroffensive as a decisive battle, describing the war against Russia’s invasion as a long series of operations.

“We said throughout that this would be a tough fight, it would be a long fight and it will see challenges, successes and setbacks,” US Secretary of Defense Lloyd Austin told reporters Thursday at a news conference in Papua New Guinea. “They’ve been working their way to get through the minefields and other obstacles, but they still have a lot of combat power.”

Wheat futures climbed as Ukraine said Russia fired two Kalibr cruise missiles from a submarine in the Black Sea at Odesa region port infrastructure, damaging equipment at a cargo terminal and increasing concerns over Black Sea grain supplies.

Read More: Wheat Jumps After Russian Strike Boosts Black Sea Supply Fears

Wheat in Chicago rose 2.5% to $7.3825 a bushel by 3:26 p.m. Singapore time. Prices of the food staple are extremely sensitive to news of Russian attacks on Ukrainian ports because of the global importance of crop supplies from the Black Sea region. 

Russia pulled out of an agreement that allowed Ukraine to ship grain through the Black Sea on July 17, and has since attacked infrastructure at Odesa region ports, as well as on the Danube river. 

--With assistance from Jennifer Jacobs and Matthew Brockett.

(Updates with grain prices starting in second paragraph.)

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