A US State Department spokesman revealed Thursday that Russian officials had trained in Iran over the past few weeks as part of an agreement between Tehran and Moscow related to the transfer of drones.
Last month, US officials had expressed their belief that Iran was preparing to supply Russia with up to several hundred drones, including those that could be armed, noting that Russian officials had visited Iran to see attack drones.
The claim has raised concerns that Iran, which supplies drones to its Middle Eastern allies, is now supporting Russia in its war in Ukraine.
The Iranian foreign minister denied the allegation at the time, and even phoned his Ukrainian counterpart to assure him that this would not happen.
"Russian officials have conducted training in Iran over the past several weeks," Deputy State Department spokesman Vidant Patel told reporters during a telephone briefing Thursday.
He added that the United States would "vigorously enforce" its sanctions on Russian and Iranian arms trade.
Patel said transfers of drones between the two countries are "potentially subject to sanctions under various authorities."
The US spokesman expressed Washington's concern about Iran's use and spread of drones.
"It has been used to attack US forces, our partners in the region, and international shipping entities," he added.