The US believes Russian officials have begun training on drones in Iran over the last several weeks, the latest sign that Russia intends to purchase the systems as the war in Ukraine continues.

"During the last several weeks, Russian officials conducted training in Iran as part of the agreement for UAV transfers from Iran to Russia," a US official told CNN. The official said the intelligence about the training has recently been declassified.

CNN has reached out to the Russian embassy in Washington for comment. Kremlin spokesperson Dmitry Peskov said last month that Russia had "no comments on the matter" when asked by reporters about the drones.

CNN first reported last month that a Russian delegation had visited an airfield in central Iran at least twice since June to examine weapons-capable drones, according to national security adviser Jake Sullivan and satellite imagery obtained exclusively by CNN.

Iran began showcasing the Shahed-191 and Shahed-129 drones, also known as UAVs or Unmanned Aerial Vehicles, to Russia at Kashan Airfield south of Tehran in June, US officials told CNN. Both types of drones are capable of carrying precision-guided missiles. Sullivan said in July that the US believes Iran intends to sell Russia hundreds of the drones that Russia can use in

The Ukrainian military has primarily been deploying Turkish-built Bayraktar UAVs to destroy Russian command posts, tanks and surface-to-air missile systems, while the Russians have been using homemade Orlan-10 drones for reconnaissance and electronic warfare.

But the Russians have been struggling to replenish their supply, leading them to turn to Iran for the equipment, the US believes. US officials have also argued that the growing relationship between Iran and Russia exemplifies why the US needs to maintain its presence and influence in the Middle East.

Ukraine, meanwhile, has pleaded with the US to provide more powerful armed drones like the Gray Eagle, but the US has been reluctant to provide them for fear that Russia could view it as overly escalatory.