"North Korea and Russia are two independent sovereign states. How they develop bilateral relations is their own matter," Beijing's foreign ministry spokesman Lin Jian said.

Seeking advantage in his grinding invasion of Ukraine, President Vladimir Putin has brought in troops and military hardware from North Korea, the first time Russia has invited foreign forces on its soil in more than a century.

Citing US intelligence, Secretary of State Antony Blinken said that about 8,000 of the 10,000 North Korean troops believed to be in Russia have made their way to the Kursk border region.

Ukrainian President Volodymyr Zelensky has denounced what he called inaction by his allies on North Korean troops and said he was surprised by the "silence" of China.

In response, Beijing said Friday it "does not know the specific situation of bilateral exchange and cooperation between North Korea and Russia".

"China's position of hoping various parties will promote an easing of the situation and work for a political solution to the Ukraine crisis has not changed," Lin said.