Iranian troops have been training Russian forces in Crimea in the use of Tehran-made drones to strike Ukrainian cities including Kyiv, White House National Security spokesman John Kirby confirmed on Thursday.
He added that the US is currently no longer focusing on diplomacy with Iran over a proposed new nuclear deal.
“We can confirm that Russian military personnel that are based in Crimea have been piloting Iranian [drones], using them to conduct strikes across Ukraine including strikes against Kyiv in just recent days,” Mr Kirby told reporters.
“We assess that Iranian military personnel were on the ground in Crimea and assisted Russia in these operations.”
He said Russia had received “dozens” of Iranian unmanned aerial vehicles so far and will probably receive additional shipments in the future.
“Furthermore, in light of Russia's ongoing supply shortages, we are concerned that Russia may also seek to acquire advanced conventional weapons from Iran, such as surface-to-surface missiles that will almost certainly be used to support the war against Ukraine,” Mr Kirby said.
He added that President Joe Biden's administration would look for ways to make it harder for Tehran to sell such weapons to Russia and added that the US is no longer focused on diplomacy and nuclear talks with Iran.
“We are way far apart with the Iranians in terms of a return to the [nuclear] deal. So we're just simply not focused on that right now,” he said.
“What we are focused on is making sure that we are holding the regime accountable for the way they're treating peaceful protesters in their country and supporting those protesters.”
Mr Kirby was referring to the violent crackdown on the women-led anti-government protests that have followed the death of 22-year-old Mahsa Amini in police custody.
In recent weeks, Ukrainian forces have released images of what analysts say is the wreckage of Iranian-made Shahed-136 drones that have been fired at targets across the country.
Iran has denied it is supplying Russia with drones. The White House on Thursday said both Tehran and Moscow are lying.
“Both Iran and Russia continue to lie about it, denying that Iran is providing weapons to Russia for use in Ukraine … They can lie to the world but they certainly can't hide the facts,” said Mr Kirby.
Pentagon spokesman Brig General Pat Ryder gave a similar assessment to Mr Kirby.
"We continue to see Iran complicit in terms of exploiting terror, not only in the Middle East region but now also in Ukraine," he said.
Ukraine capital Kyiv hit by kamikaze drones — in pictures
Earlier on Thursday, Moscow's foreign ministry accused the West of “pressuring” Tehran with those accusations.
“Everything that is now being done on the Iranian track is subordinated to one goal — pressure on this country,” ministry spokeswoman Maria Zakharova said at a press briefing.
“And Washington is mobilising Nato and EU countries for this in support of its position.”
The European Union on Thursday announced sanctions against three Iranian generals and an arms firm accused of supplying Iranian drones to Russia.
The White House announcement came a day after Moscow said it would reassess co-operation with UN Secretary General Antonio Guterres if he sends experts to Ukraine to inspect drones.
