Russia appears to be massing tens of thousands of troops in the southern Ukrainian city of Kherson as Ukraine has stepped up counteroffensives in the country's east and south.

The Ukrainian forces announced on Sunday that they had successfully repulsed Russian troops in 10 districts of the eastern Donetsk region.

The Ukrainians are believed to be advancing to the city of Kherson, the main city in the Kherson region.

Ukrainian media reported on Saturday the view of a top official of the country's military intelligence unit that Russia is moving 40,000 troops toward Kherson. Many of the troops are believed to belong to elite units, including airborne forces.

The official said that it will likely take about a month for Ukrainian troops to liberate Kherson.

In an interview with NHK last week, Ukrainian Defence Minister Oleksii Reznikov conveyed a similar view that the Russian military was deploying units in Kherson and surrounding areas.

Meanwhile, Russia announced that it had indefinitely suspended its participation in a deal that facilitated agricultural exports from Ukraine.

Moscow said it can no longer guarantee the safety of cargo ships participating in the deal, citing a drone attack on its Black Sea Fleet in Crimea.

The Russian defense ministry said on Sunday that the launch of drones was carried out from the coast near the southern city of Odesa.

The Ukrainian government has not officially reacted to the Russian claim.

Ukraine's foreign minister Dmytro Kuleba tweeted on Sunday, "The pattern of Russian behavior is so predictable." He wrote, "Yesterday they put millions of people at the risk of hunger, today they imitate readiness for negotiations. No one should get fooled by this."