The US on Friday expressed alarm over a “full-scale defence partnership” between Russia and Iran, describing it as “harmful” to Ukraine, Tehran's neighbours and the world.
Iran stands accused by western powers of supplying drones to Russia for its war against Ukraine, as Moscow batters the country's energy infrastructure in search of an advantage in the bloody conflict.
“Russia is seeking to collaborate with Iran in areas like weapons development, training,” White House National Security spokesman John Kirby told reporters.
Russia “is offering Iran an unprecedented level of military and technical support — that is transforming their relationship into a fully fledged defence partnership”, he told reporters.
“We have also seen reports that Moscow and Tehran are considering the establishment of a joint production line for lethal drones in Russia. We urge Iran to reverse course [and] not to take these steps.”
Mr Kirby said that the US would sanction three Russian-based entities active in “the acquisition and use of Iranian drones”.
Last month, Tehran admitted it had sent drones to Russia, but insisted they were supplied before the invasion of Ukraine.
The State Department on Friday announced sanctions on three Russian entities connected to Moscow’s growing military relationship with Tehran.
"The Kremlin is deploying these UAVs [unmanned aerial vehicles] against Ukraine, including in large-scale attacks on civilian infrastructure," said Secretary of State Antony Blinken in a statement.
He added that Russia’s acquisition and Iran’s provision of the drones are in breach of UN Security Council rules and further fuels the conflict in Ukraine.
"The United States will continue to use every tool at our disposal to disrupt these transfers and impose consequences on those engaged in this activity," he said.
In his remarks on Friday, Mr Kirby also announced a new $275 million aid package to help boost Ukraine's air defences against Russian drones in particular.
He said the aid “will soon be on its way to provide Ukraine with new capabilities to boost its air defences and counter the threats that Ukraine is facing from drones”.
Meanwhile, in London, British Foreign Secretary James Cleverly said Iran is now one of Russia’s top military backers.
“Their sordid deals have seen the Iranian regime send hundreds of drones to Moscow, which have been used to attack Ukraine’s critical infrastructure and kill civilians,” he said in a statement.
“In return, Russia is offering military and technical support to the Iranian regime, which will increase the risk it poses to our partners in the Middle East and to international security.”
Agence France-Presse contributed to this report