A top U.S. official on North Korea held a video call this week with China’s envoy on Korean Peninsula affairs in which they discussed the growing military cooperation between Moscow and Pyongyang, the State Department said Friday.

The U.S. senior official for North Korea, Jung Pak, and her Chinese counterpart, Liu Xiaoming, also addressed North Korea’s “increasingly destabilizing and escalatory behavior,” the department said in a statement.

It said the growing military cooperation between Russia and North Korea was “in violation of numerous U.N. Security Council resolutions.”

Russia has long been party to U.N. sanctions on North Korea over the latter’s ballistic missile and nuclear weapons programs but has stepped up ties with Pyongyang since invading Ukraine in 2022.

The United States has accused North Korea of supplying Russia with artillery shells and missiles used in Ukraine.

Moscow and Pyongyang deny the accusations but vowed last year to deepen military relations.

The State Department said the video call followed a February 16 meeting between U.S. Secretary of State Antony Blinken and Chinese Foreign Minister Wang Yi in Munich at which they “affirmed the importance of continued communication on [North Korea] issues at all levels.”

The Kremlin on Tuesday said Russian President Vladimir Putin had given North Korean leader Kim Jong Un a Russian Aurus limousine as a gift. On Friday, Washington imposed sanctions on the producer of the car as part of a sweeping round of sanctions against Russia over the death of opposition leader Alexey Navalny and to mark the second anniversary of the invasion of Ukraine.

The sanctions and trade restrictions also targeted Chinese firms that the U.S. said were assisting Russia’s war.

Sino-U.S. relations have shown signs of improvement in recent months with steps to reestablish communication channels after ties sank to their lowest levels in decades.

But many points of friction remain, including U.S. sanctions on China over security and human rights issues. China said Wang told Blinken in Munich that these should be lifted.

The top U.S. official for arms control, Bonnie Jenkins, told an event on Thursday that Washington was keen for more talks with China on strategic stability and crisis management and that a more aggressive North Korea was not in Beijing’s interest.

She said she believed North Korea, which borders China, is keen to acquire fighter aircraft, surface-to-air missiles, armored vehicles, ballistic missile production equipment or materials and other advanced technologies from its cooperation with Russia.