The White House on Friday warned that Russia may provide Iran with fighter jets as part of an expanding defense relationship between the two countries.

John Kirby, a White House spokesperson on national security issues, told reporters in a virtual briefing that the U.S. has “additional information” that Iran’s support for Russia’s war in Ukraine is growing. 

In return, Kirby said, Russia has been offering Iran “unprecedented support,” and the U.S. government believes Moscow may provide Iran with fighter jets. Iran is additional looking to purchase billions of dollars worth of equipment from Russia, such as helicopters and radar.

“We’re going to be watching this very closely to see what, if anything, actually transpires and what, if any, transactions are actually made,” Kirby said.

“There is this growing defense cooperation between Iran and Russia, and it’s not only certainly going to make things in Ukraine more difficult, but it could certainly make the security situation in the Middle East more difficult,” Kirby added.

The White House has previously warned of deepening military ties between Russia and Iran amid Russia’s ongoing invasion of Ukraine.

National security adviser Jake Sullivan said last July that Iran was preparing to provide Russia with hundreds of unmanned drones for use in Ukraine. 

And last November, CNN reported that Iran was preparing to send additional weapons to Russia, including short-range missiles.

Kirby said in December that U.S. believed Moscow and Tehran “are considering the establishment of a joint production line for lethal drones in Russia.”

Friday marked one year since Russia launched its unprovoked invasion of Ukraine. The Biden administration announced a fresh raft of sanctions targeting the Russia economy in conjunction with the anniversary, as well as a new package of military and economic assistance for Ukraine.