The White House said on Friday that Russia appeared to be deepening its defense cooperation with Iran and had received hundreds of one-way attack drones that it is using to strike Ukraine, Reuters reported.

Citing newly declassified information, the White House said the drones or Uncrewed Aerial Vehicles (UAVs) were built in Iran, shipped across the Caspian Sea and then used by Russian forces against Ukraine.

“Russia has been using Iranian UAVs in recent weeks to strike Kyiv and terrorize the Ukrainian population, and the Russia-Iran military partnership appears to be deepening,” White House spokesman John Kirby said in a statement.

“We are also concerned that Russia is working with Iran to produce Iranian UAVs from inside Russia.”

Kirby said the United States had information that Russia was receiving materials from Iran required to build a drone manufacturing plant that could be fully operational early next year.

“We are releasing satellite imagery of the planned location of this UAV manufacturing plant in Russia’s Alabuga Special Economic Zone,” he said.

Support between the two countries was flowing both ways, Kirby said, with Iran seeking billions of dollars worth of military equipment from Russia including helicopters and radars, read the report.

“Russia has been offering Iran unprecedented defense cooperation, including on missiles, electronics, and air defense,” he said.

“This is a full-scale defense partnership that is harmful to Ukraine, to Iran’s neighbors, and to the international community. We are continuing to use all the tools at our disposal to expose and disrupt these activities including by sharing this with the public – and we are prepared to do more.”

Kirby said the transfers of drones constituted a violation of United Nations rules and the United States would seek to hold the two countries accountable.

The U.S. has previously sanctioned Iranian executives at a defense manufacturer over drone supplies to Russia. Iran has acknowledged sending drones to Russia but said in they past they were sent before Russia’s February invasion, Reuters reported.

“We will continue to impose sanctions on the actors involved in the transfer of Iranian military equipment to Russia for use in Ukraine,” Kirby said.

He said a new U.S. advisory would be issued on Friday “to help businesses and other governments better understand the risks posed by Iran’s UAV program and the illicit practices Iran uses to procure components for it.”