KYIV, July 13 (Reuters) - Ukraine has received cluster bombs from the United States, munitions banned in more than 100 countries, but has pledged to only use them to dislodge concentrations of enemy soldiers.

Valeryi Shershen, a spokesman for the Tavria, or southern, military district on Thursday confirmed an announcement by his commander that the weapons had arrived a week after the United States said it would send them as part of an $800-million security package.

The Pentagon also announced their arrival.

Moscow has denounced their shipment. Defence Minister Sergei Shoigu warned on Thursday that Russia could resort to deploying similar weaponry if faced with their use.

Ukrainian officials say their deployment is justified in view of Russia's mining of vast tracts of land it has seized.

Ukraine has launched a counter offensive more than 500 days into the war, focusing on capturing groups of villages in the southeast and retaking areas around the eastern city of Bakhmut, seized by Russian forces in May after months of fighting.

"This will further demotivate Russian occupying forces and fundamentally change things in favour of the Ukrainian armed forces," Shershen told U.S.-funded Radio Liberty.

The munitions, he said, would be used strictly within the legal framework, "only for the deoccupation of our territories.

"They will not be used on Russian territory...They will be used only in areas where Russian military forces are concentrated in order to break through enemy defences."

President Volodymyr Zelenskiy restated Ukraine's assurances during a NATO summit on Wednesday.

Cluster munitions typically release large numbers of smaller bomblets that can kill indiscriminately over a wide area. Those that fail to explode pose a danger for decades.

Each side has accused the other of using cluster bombs in the conflict launched by Russia's invasion in February 2022.

Human Rights Watch says both Moscow and Kyiv have used cluster munitions. Russia, Ukraine and the U.S. have not signed up to the Convention on Cluster Munitions, which bans production, stockpiling, use and transfer of the weapons.

The decision to send the munitions to Ukraine has been opposed by Spain and Canada, while Britain said it was part of a convention that discourages use of the weapons. Some U.S. Democratic lawmakers also raised their concerns.

Ukrainian military analyst Oleskander Musiyenko said he assumed the weapons would be used in the south as that area's commander had announced their arrival.

"We can say that it is in the south where it is planned to pierce and destroy the fortifications of the enemy's defence line," Musiyenko told Ukrainian television. "I think cluster munitions will expand the capabilities of our troops."

Deputy Ukrainian Defence Minister Hanna Maliar said Ukrainian troops were making headway in the south, forcing enemy forces to redeploy. Near Bakhmut, Ukrainian troops made gains south of the city, but faced more difficulties to the north.

Russian accounts of the fighting said its forces had repelled 16 Ukrainian attacks in eastern Donetsk region alone.