Missiles fired by Russia in two attacks on Ukraine within the past week were supplied by North Korea, the White House said Thursday.
"Our information indicates that the Democratic People's Republic of Korea recently provided Russia with ballistic missile launchers and several ballistic missiles," United States National Security Council spokesperson John Kirby said.
Russian forces launched at least one of the North Korean-supplied missiles on 30 December, which landed in an open field in the Zaporizhzhia region, according to the spokesperson.
Moscow's forces then fired "multiple" ballistic missiles into Ukraine as part of a mass aerial attack on 2 January, he added.
"This is a significant and concerning escalation of the DPRK's support for Russia," Kirby said.
The development underscored the need for the US Congress to pass a package of vital military aid for Ukraine, without which the pipeline of support will soon run dry, he said.
Air defenses for Ukraine, which has come under a barrage of aerial attacks by Russia in recent days, were "absolutely" a priority, he said.
"It's critical that Congress meets this moment and responds by providing the Ukrainians what they need to defend themselves. The time for Congress to act is now," Kirby said.
The US and its allies will now raise the matter at the United Nations Security Council as it represents a breach of UN sanctions against North Korea, he added.
North Korea would pay a "high price" for breaching UN sanctions, Britain's Foreign Office said in a statement.
Meanwhile, Russia's defense ministry said Friday it repelled a Ukrainian attack over Crimea on the same day, shooting down 36 drones over the annexed peninsula.
The ministry said in a statement on Telegram that its air defense systems "destroyed and intercepted" 36 Ukrainian drones over Crimea, a peninsula that Russia annexed in 2014 and which Kyiv has vowed to reclaim.
Another Ukrainian drone over Russia's western Krasnodar region was destroyed, the ministry added.