Russia has fired ballistic missiles provided by North Korea into Ukraine in recent days, the White House confirmed on Thursday, calling it a “worrying escalation” in Pyongyang’s support for Moscow.

The United States noted that North Korea had recently provided Russia with a missile launcher and several ballistic missiles, John Kirby, a White House national security spokesman, told reporters.

Russia used at least one of those missiles in an attack on Ukraine on Dec. 30, 2023, and several more in an attack on Tuesday, Kirby said.

“We expect Russia and North Korea to learn from these launches, and we expect that Russia will use additional North Korean missiles to attack Ukraine’s civilian infrastructure and kill innocent Ukrainian civilians,” he said.

Kirby said the U.S. determined that the Dec. 30 missile appeared to have landed in an open field in Ukraine. Officials are still assessing the impact of the Jan. 2 launch, he said.

“This is a significant and concerning escalation of the DPRK’s support for Russia,” Kirby said.

National Security Council Speaker John Kirby speaks to reporters during the daily briefing at the White House in Washington, DC on Wednesday, January 3, 2024. Kirby discussed, among other things, the situation in Iran and Israel-Palestine.

Kirby said the U.S. believes North Korea wants fighter jets, surface-to-air missiles and other advanced technologies to improve its own military capabilities in return for supplying Russia with ballistic missiles.

The White House has been warning for months about a burgeoning partnership between North Korea and Russia as Moscow wages its war against Ukraine. North Korea in October delivered more than 1,000 containers with ammunition and other equipment to Russia.

“Partly because of our sanctions and export controls, Russia has become increasingly isolated on the world stage and forced to turn to like-minded states for military equipment,” Kirby said Thursday. “As we have publicly warned, North Korea is one of these states.”

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Moscow’s escalation comes after the White House acknowledged it had run out of approved funds to provide military aid to Ukraine to defend itself against invading Russian forces.

The Biden administration announced a last round At the end of December, $250 million was allocated to strengthen Ukraine’s air defense capabilities and provide additional equipment. But White House officials have stressed that the U.S. will not be able to approve additional aid without action from Congress.

According to Ukrainian President Volodymyr Zelensky, Russia fired around 500 missiles and drones from December 29 to January 2 as Moscow steps up its winter offensive. Dozens of Ukrainian civilians were killed and hundreds more injured in the attacks.

Updated at 1:37 p.m