"These UAVs are used by Russia in its war of aggression against Ukraine to attack civilian infrastructure and cities in Ukraine, resulting in the deaths of innocent civilians," the letter said.

Ukraine says it has shot down more than 200 Iranian drones over the country since mid-September. The United States also accused the Iranian military on Thursday of having supported Russia in drone operations against Ukraine from Crimea.

The Kremlin denies using Iranian drones in Ukraine. Iran also rejects the reports as "unsubstantiated allegations".