The US said Thursday that Russian officials have undergone training in Iran in recent weeks as part of an agreement on the transfer of drones from the Islamic Republic.

US State Department deputy spokesperson Vedant Patel reiterated during a phone briefing that Russian officials had conducted training on drones in Iran "in the last several weeks."

He said Washington would "vigorously enforce" its sanctions on both Russian and Iranian weapons trading as the transfers of drones between the two countries was "potentially sanctionable under numerous authorities," noting that "We remain incredibly concerned about Iran's use and proliferation of UAVs. They have been used to attack US forces, our partners in the region, and international shipping entities.”

Since last month, US officials have repeatedly said that Washington had information that Iran was preparing to provide Russia with up to several hundred drones, including some that are weapons capable, and that Russian officials had visited Iran to view attack-capable unmanned aerial vehicles (UAVs)

Iran has been supplying drones to its allies in the Middle East for a long time but selling drones to Russia to for its war in Ukraine has raised serious international concerns.

Iran's foreign minister denied the claim, including in a phone call with his Ukrainian counterpart but late In July, an Iranian lawmaker said the military cooperation between Tehran and Moscow has upset the political equations of the global order, confirming Russia’s request to buy Iranian drones.

US National Security Adviser Jake Sullivan warned twice in July that Moscow appears to be looking at buying Iranian drones and Russian officers even visited a drone base in Iran’s Kashan to review their options.

An adviser to President Volodymyr Zelensky told Iran International on July 25 that Russia and Iran are allies in the Ukraine war and it won’t be a surprise if Tehran supplies drones to Moscow.