The United States has been in touch with European allies on reports that Iran is "planning to deliver hundreds of ballistic missiles to Russia," State Department spokesman Vedant Patel told reporters.

"We are prepared to deliver a swift and severe response if Iran were to move forward with the transfer of ballistic missiles, which would, in our view, represent a dramatic escalation in Iran's support for Russia's war of aggression against Ukraine," he said.

Russia has been turning to countries under international sanctions, including North Korea, for military equipment to support its operations in Ukraine.

The United States has previously imposed sanctions on suppliers of Iranian drones, or unmanned aerial vehicles (UAVs), to Russia.

"Iranian officials also continue to deny providing any UAVs to Russia when evidence is plain for the world to see that Russia has used these UAVs in relentless attacks against the civilian population in Ukraine, against civilian infrastructure," Patel said.

He noted that Iranian President Masoud Pezeshkian, considered a reformist within the clerical state, had campaigned with hopes of improving relations with the United States and European countries.

"This duplicity is only the latest reminder to the international community that the Iranian regime lacks in credibility," he said.