Russia-Ukraine updates: Russian missiles hit close to nuclear reactors: IAEA director

The Ukrainian Armed Forces said on Monday Russian troops were massing in the direction of the town of Kryvyi Rih in the Dnipropetrovsk region, possibly in a bid to prepare for a large Ukrainian counterattack.

Talk of a major Ukrainian counteroffensive aimed at taking back the southern city of Kherson, about 140 miles south of Kryvyi Rih, has been gathering pace for several weeks.

The Ukrainian military also issued the maximum missile-fire-threat alert on Sunday in reaction to Russian troops massing in the Black Sea.

At least 17 warships and boats of the Russian Black Sea fleet were maneuvering near the Crimean coast on Sunday, according to Ukrainian military officials.

Among them were six Kalibr cruise missile carriers with more than 40 high-precision missiles on board, as well as four large landing ships.

Russia has also been transferring a large number of troops to occupied Crimea, Vadym Skibitskyi, of the Ukrainian Ministry of Defense, said on Monday.

Russia plans to deploy these troops in the south of Ukraine to conduct future combat operations, Skibitskyi said.

The official added that Russia withdrew tactical groups of airborne troops from the eastern Donetsk region and transferred them to occupied Kherson about two weeks ago.

Russian forces have resumed localized ground attacks northwest and southwest of Izyum over the weekend and may be setting conditions for offensive operations further west into Kharkiv Oblast or toward Kharkiv City, the Institute for the Study of War said in its latest report.

-ABC News' Edward Szekeres, Yulia Drozd and Max Uzol

Ukrainian Minister of Foreign Affairs Dmytro Kuleba called Monday a "day of relief for the world" as his country resumed grain shipments for the first time since Russia's offensive began.

"The day of relief for the world, especially for our friends in the Middle East, Asia, and Africa, as the first Ukrainian grain leaves Odesa after months of Russian blockade," Kuleba wrote in a post on Twitter. "Ukraine has always been a reliable partner and will remain one should Russia respect its part of the deal."

Watching as the first ship carrying Ukrainian grain set off from Odesa's port on Monday morning, Ukrainian lawmaker Oleksiy Honcharenko called it "Ukraine's victory" over Russia.

Honcharenko, the son of a former Odesa mayor, said this "historic moment" was only possible because Ukraine had inflicted so much damage on the Russian Navy and had liberated nearby Snake Island, forcing Russian President Vladimir Putin to make a deal.

"It shows again the the language of force is the only language Putin understands," Honcharenko told ABC News.

Honcharenko said he believes 16 more ships in the port will now begin moving out in the coming days. But he cautioned that he thinks Putin will now try to do everything to limit the ships coming in and out to a minimum within the U.N.-brokered deal, utilizing airstrikes near Ukrainian ports as well as trying to invent bureaucratic obstacles.

The next big test of the deal will be when the first ships come to enter Odesa, which Honcharenko said is expected at the end of this week.

-ABC News' Dragana Jovanovic, Oleksii Pshemyskiy and Patrick Reevell

The first ship carrying Ukrainian grain departed Odesa on Monday morning under an internationally brokered deal attempting to ease a global hunger crisis.

The Sierra Leone-flagged cargo ship Razoni left the Ukrainian port city and is headed to Lebanon, a tiny Mideast nation that imports nearly all of its grain and lacks storage space after a 2020 explosion destroyed grain silos at its main port in Beirut. The vessel is expected to reach Istanbul on Tuesday, where it will be inspected before being allowed to proceed to Tripoli, according to a statement from the Turkish Ministry of National Defense.

Razoni, which is carrying 26,527 tons of corn, is the first commercial ship to set off from Ukraine's port of Odesa since Feb. 26 and the first vessel to depart under the so-called Black Sea Grain Initiative, according to a statement from the spokesperson for the the United Nations secretary-general. Last month, Russia and Ukraine signed separate agreements with Turkey and the U.N. to allow Ukraine to resume its shipment of grain from the Black Sea to world markets and for Russia to export grain and fertilizers.

Since Russian forces invaded neighboring Ukraine on Feb. 24, the cost of grain, fertilizer and fuel has skyrocketed worldwide. Russia and Ukraine -- often referred to collectively as Europe's breadbasket -- produce a third of the global supply of wheat and barley, but a Russian blockade in the Black Sea combined with Ukrainian naval mines have made exporting siloed grain and other foodstuffs virtually impossible. As a result, millions of people around the world -- particularly in Africa and the Middle East -- are now on the brink of famine.