According to Russian President Vladimir Putin, Russia possesses a “sufficient stockpile” of cluster bombs. He also said that Russia “withholds the right to execute reciprocal action” if Ukraine uses the contentious weapons.

In his initial remarks on the U.S.’s delivery of cluster bombs to Ukraine, Putin claimed that Russia had not yet utilized cluster bombs in its ongoing conflict in Ukraine.

Although both Russia and Ukraine had deployed cluster bombs, and it had been widely documented by The AP and international humanitarian groups, he said, “Until now, we haven’t done this, we haven’t used it, and we haven’t had such a necessity.”

Cluster bombs sent by the United States have arrived in Ukraine, according to a statement from the Pentagon on Thursday.

The munitions, which are bombs that will explode in the air and then scatter dozens of smaller bomblets, are viewed by the U.S. as a way of providing Kyiv with the weapons it desperately requires to reinforce its attack to break through Russian defenses. President Biden made the ultimate choice this week after months of heated discussion among American officials.

As a result of its high “dud rate,” or the tendency to often leave unexploded bomblets behind that might hurt civilians long after a war has finished, cluster bombs have long been condemned by humanitarian organizations and several U.S. allies.

The weapons the U.S. is sending have been upgraded so that they leave behind much fewer unexploded rounds, according to supporters, who claim that Russia has already been employing cluster bombs in Ukraine. Ukraine has committed to solely using them away from heavily populated regions.