Washington DC - Ukraine is now using the cluster munitions supplied by the United States, and their use is already helping with the country's defense against Russia, US National Security Council communications director John Kirby said on Thursday.

"They are using them appropriately, they are using them effectively," Kirby claimed. For additional details, Kirby referred to the Ukrainians.

Cluster munitions are missiles or bombs that burst in the air over the target and disperse many small explosive devices. A significant proportion of them do not detonate, but remain on the ground as unexploded ordnance. More than 100 countries have outlawed their use.

The Biden administration's decision to send cluster bombs to Ukraine sparked backlash from many Democrats and Republicans in Congress.

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Russian President Vladimir Putin had threatened to use cluster munitions if Ukraine started using them, but many experts believe the Kremlin has already deployed such munitions in its war against Ukraine.

As the Russia-initiated war nears 17 months, the US imposed fresh sanctions on 120 individuals and companies that support Russia and are aimed at impairing Russia's energy production and export capabilities.

Also on Thursday, UN Secretary General António Guterres condemned "in the strongest terms" the repeated Russian attacks on the port of Odessa and other Ukrainian cities on the Black Sea.

He told the attacks violate an agreement Russia signed with the UN. Ukraine said the attacks destroyed 60,000 tons of grain being stored on the Black Sea coast.

The UN chief also criticized Russia's suspension on Monday of an agreement to export Ukrainian grain from the Black Sea, saying it was contrary to commitments Russia made to the UN and was already having a negative impact on global wheat and maize prices.

The UN Security Council is to discuss the provisional end of the grain agreement in a special session on Friday.