A US military official says Ukraine has received cluster munitions, less than a week after the United States pledged to transfer the controversial weaponry to Ukrainian forces.
US Lieutenant General Douglas Sims on Thursday said the "cluster munitions are in Ukraine."
Asked about the slower pace of advance in Ukraine's counteroffensive, he told journalists that "this is hard warfare, it's in really tough terrain, it's under fire".
"When you consider all that, it's pretty remarkable," he added.
The US announced on July 7 it would send Kiev cluster munitions as part of an $800-million security package intended to help Ukrainian forces against Russia, despite concerns over the long-term risk posed to civilians by bomblets that fail to explode.
A Ukrainian army commander on Thursday confirmed the news.
"We just got them, we haven't used them yet, but they can radically change (the battlefield)," Ukrainian army commander Oleksandr Tarnavskyi told US broadcaster CNN.
"The enemy also understands that with getting this ammunition, we will have an advantage," Tarnavskyi said.
He added that Ukrainian forces would not deploy the weapon in heavily populated areas.
Russia vowed to respond with countermeasures if Kiev uses the munitions against its forces.
“The potential use of this type of munitions changes the situation, and of course, it would force Russia to take countermeasures,” Kremlin spokesman Dmitry Peskov told reporters on Wednesday, without providing details “countermeasures” would entail.
US President Joe Biden said last week that the decision to provide the munitions was "very difficult," but that Ukrainian forces were "running out of ammunition."
"They either have the weapons to stop the Russians now -- keep them from stopping the Ukrainian offensive through these areas -- or they don't. And I think they needed them," he said.
The Pentagon said in a statement that the new military aid package announced on July 7 included "dual-purpose improved conventional munitions," referring to cluster munitions.
Washington’s decision was opposed by many countries across the world, including its Western allies.
Cluster bombs are banned under the Convention on Cluster Munitions (CCM), an international treaty that addresses the humanitarian consequences and unacceptable harm caused to civilians by cluster munitions through a categorical prohibition and a framework for action.
The weapons can contain dozens of smaller bomblets, dispersing over vast areas, often killing and maiming civilians. The CCMs are banned because unexploded bomblets can pose a risk to civilians for years after the fighting is over.
Cluster munitions generally eject submunitions that can cover five times as much area as conventional bombs.
The Convention on Cluster Munitions, which took effect in 2010, bans all use, production, transfer and stockpiling of cluster bombs. More than 100 countries have signed the treaty, but the US, Russia and Ukraine have not.