US Special Envoy for Iran Robert Malley has rejected a claim by Iran's foreign minister that Tehran supplied drones to Russia prior to its invasion of Ukraine.

In a tweet Sunday, Malley was reacting to Hossein Amir-Abdollahian's admission that Iran provided military drones to Russia, but before the Ukraine war. Tehran's top diplomat said his government will act if evidence exists of Iranian drones being used in the war.

Malley, however, said that "Iran didn’t give a limited number of drones before the war. They transferred dozens just this summer & have military personnel in occupied Ukraine helping Russia use them against Ukrainian civilians. Confronted with evidence, they need a new policy, not a new story."

The United States warned in July that Iran was preparing to supply drones to its ally Russia, as the war in Ukraine was going badly for Moscow. By October, Ukraine was showing evidence of dozens of Iranian Shahed-136 suicide drones targeting its infrastructure and cities.

Europe and the US have adopted a tough position on the issue, warning of more sanctions against the Islamic Republic.

Tehran first denied it had supplied weapons to the warring sides in Ukraine but has now admitted that it has supplied drones without any specifics.

In recent days reports have emerged claiming that Tehran is also preparing to supply ballistic missile to Moscow, as its stockpile of conventional missiles are running low.

Iran is already subject to US oil export and international banking sanctions over its nuclear program.