Russia has stocked up on Iran with hundreds of Iranian drones. But according to the United States, cooperation between Tehran and Moscow is not limited to arms deliveries. On the Crimean peninsula, the cooperation extends to training and technology.

According to the United States, the Iranian military has supported Russia in drone operations against Ukraine from Crimea. “Our assessment is that Iranian military forces have been in Crimea and assisted Russia in these operations,” US National Security Council spokesman John Kirby said of the recent drone strikes against Ukraine.

The Iranians would train and provide technical support to the Russians, while Russians piloted the drones. “Tehran is now directly involved on the ground,” Kirby told journalists. Tehran also supplies Russia with weapons that “affect civilians and civilian infrastructure in Ukraine.” Kirby announced the US would continue to enforce all sanctions against Russia and Iran’s arms trade.

The European Union recently tightened its sanctions against Tehran because of the delivery of Iranian drones to Russia. Ukraine says it shot down more than 230 Iranian drones over the country last month. The Kremlin denies using Iranian drones in Ukraine. Russia illegally annexed the Ukrainian peninsula of Crimea in 2014.