The United States said Monday there are signs that Russia and Iran are expanding their military cooperation.

State Department spokesperson Vedant Patel told reporters that Iran “remains Russia’s top military backer, and Iran has already provided Russia with artillery and tank rounds for use in Ukraine.”

Patel said that since August, “Iran has provided Russia with more than 400 UAVs, primarily of the Shahed variety, and Russia has expended most of these UAVs using them to target Ukrainian critical infrastructure inside Ukraine.”

“The deepening of this cooperation is a threat and a danger to not just Ukraine; it’s a threat and a danger to Russia’s neighbors, Iran’s neighbors, and the international community broadly,” Patel told reporters.

White House National Security Council spokesman John Kirby told reporters during a Monday briefing that the Russia-Iran ties allow Russia to kill more people in Ukraine while enabling Iran to stockpile military hardware and pose a greater threat to its neighbors.

Some information for this report came from Reuters.