Russia has a stockpile of cluster munitions and will consider using them against Ukraine "if they are used against us," President Vladimir Putin said.
Putin's comments come just days after Ukraine received a delivery of American-made cluster munitions, though a top Ukrainian military official told CNN they had not yet been used.
"Russia has a sufficient supply of various types of cluster munitions," the Russian leader said during an interview with a pro-Kremlin journalist.
"If they are used against us, we reserve the right to mirror actions."
Washington's decision to send cluster bombs to Kyiv was controversial and criticized by human rights groups.
The weapons are particularly dangerous to civilians and noncombattants when fired near populated areas because they scatter explosive material, so-called "bomblets," across large areas. Those that fail to explode on impact can detonate years later, posing a long-term risk to anyone who encounters them, similar to landmines.
The danger posed by cluster weapons has prompted more than 100 countries -- including the United Kingdom, France and Germany -- to sign a treaty prohibiting their use.
US President Joe Biden told CNN that the decision whether to send cluster munitions to Ukraine was "very difficult," but he opted to do so because Kyiv needs more ammunition to continue its fight to push Russian troops out of Ukrainian territory.
A top official at the US Defense Department said Kyiv gave "assurances in writing" that it would not use the cluster munitions in urban areas.
In his interview, Putin said that the Biden administration had called the use of cluster munitions a war crime and that he agreed with that assessment.
It's not clear exactly which comments Putin was referring to, but former White House press secretary Jen Psaki said last year at the outset of the conflict that reports of Russia's use of cluster bombs, if confirmed, would constitute a war crime.
Putin also claimed that Russia has not yet used cluster munitions, despite evidence to the contrary.
In March, the United Nations said it had compiled credible reports that Russian forces had used cluster munitions in populated areas at least 24 times. A CNN investigation last year found that the Kremlin fired 11 cluster rockets at Kharkiv, Ukraine's second-largest city, during the war's opening days.
