Russia and Iran’s relationship has warmed to a fully fledged defence partnership, the US has said.
Russia is giving an unprecedented level of military support, said US national security council spokesman John Kirby.
The US has seen reports that the two countries are considering joint production of lethal drones, he added.
Australia has announced it is sanctioning three Iranians and one Iranian business for supplying Russia with drones to use against Ukraine.
Co-operation between Russia and Iran has been highlighted recently, with Ukraine accusing Russia of using Iranian drones in its attacks.
After initially denying sending any drones to Russia, the Middle Eastern country later admitted it had supplied some before the invasion of Ukraine.
Mr Kirby said that a partnership between Iran and Russia to produce drones would be harmful to Ukraine, Iran’s neighbours and the international community.
Writing by Omotola Oguneye