BEIJING (AFP) - Chinese President Xi Jinping has promised to promote a "long-term, sound and stable" relationship with North Korea, state news agency Xinhua said on Sunday (Oct 6), as the two countries mark 70 years of diplomatic relations.

North Korean leader Kim Jong Un also sent a message to Mr Xi saying that their countries' "invincible friendship will be immortal on the road of accomplishing the cause of socialism", Pyongyang's state news agency KCNA reported on Sunday.

North Korea was among the first countries to recognise the People's Republic of China after it was founded in 1949.

Mr Xi said the relationship between the Asian neighbours had played an "important and positive role in maintaining regional peace and stability", according to Xinhua.

Since March 2018, Mr Xi and Mr Kim have met five times.

Mr Xi became the first Chinese leader to visit the reclusive North in 14 years when he made a highly symbolic trip to the nuclear-armed state in June.

Mr Kim said the two countries would "steadily defend the cause of socialism and preserve peace and stability of the Korean peninsula and the world", according to KCNA.

The warm words from Beijing follow its huge military parade last Tuesday to mark the 70th anniversary of the founding of communist China, and come a day after the latest round of nuclear talks between the United State and North Korea ended in Sweden.

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Pyongyang - under three sets of United Nations sanctions in a bid to force it to give up its nuclear and ballistic weapons programmes - said the talks broke down because the US "disappointed us greatly".

Washington, however, said there had been "good discussions".

The talks followed months of stalemate after a February meeting between Mr Kim and US President Donald Trump, and came after Pyongyang's defiant test-fire of a sea-launched ballistic missile last Wednesday.

Since the US-North Korea talks began, Russia and China have been calling for the United Nations to start lifting sanctions so as to create momentum towards the North's denuclearisation.