Chinese President Xi Jinping stressed the importance of "friendly relations" to a visiting North Korean official Wednesday, after the envoy reportedly told Chinese officials Pyongyang would continue its internationally condemned nuclear programme.

Xi told top North Korean party official Ri Su-Yong in Beijing that "China places great value on the friendly cooperative relationship" with its isolated neighbour, an official report said.

China is North Korea's largest trading partner and has been its key diplomatic protector for decades. But relations have soured over the North's nuclear tests and long-range missile launches, with Beijing supporting UN sanctions.

According to South Korea, the North on Tuesday made an unsuccessful attempt to launch a powerful new medium-range missile.

Ri told Chinese officials on Tuesday that Pyongyang would stick to its policy of "simultaneously pushing forward economic construction and the building of nuclear force", according to the North's official KCNA news agency.

The report of the meeting between Ri -- a former foreign minister -- and Xi, which was posted on the website of the Chinese Communist Party's international department, made no mention of the nuclear issue.

It cited Xi as saying he hoped "all sides could remain calm, increase communication and dialogue and protect regional peace and stability".

Ri conveyed a message from the North's leader Kim Jong-Un in which Kim vowed to "develop the traditional friendship" between the two nations and "maintain peace and stability on the Korean Peninsula and northeast Asia", it said.

The report added that Ri updated Xi on the North's once-in-a-generation party congress last month, which cemented Kim's leadership and formally endorsed his policy of nuclear expansion.

The lack of any official Chinese representation at the congress was seen as a sign of friction between the two traditional allies.

Kim has not visited China since coming to power in December 2011 and Xi has not visited Pyongyang.

The North Korean leader watched the local Sobaeksu basketball team beat China's Olympic squad in three matches on Monday, KCNA reported.

But China's Sina Sports portal on Tuesday interviewed a Chinese Olympian who attributed the results to biased refereeing.

"At times we stood still and were accused of running, and we basically couldn't make any physical contact at all in defence," the unnamed player said.

He added: "As soon as we made contact, we were accused of a foul."