North Korean leader Kim Jong Un has vowed to keep strengthening Pyongyang's friendly ties with China in a reply message to Chinese President Xi Jinping.

On Sunday, the North's ruling Workers' Party newspaper, Rodong Sinmun, carried Kim's message, dated September 15, on the front page. It was sent in reply to Xi's congratulatory message to mark North Korea's 76th founding anniversary on September 9.

Kim starts by expressing his gratitude to Xi for extending "sincere congratulations on the occasion of the 76th birthday" of his country.

He says, "It is the common desire of the peoples of the two countries to steadily consolidate and develop" the North Korea-China friendship.

He goes on to say he is convinced that "good results will be continuously made in accomplishing the common cause of the two parties."

South Korea's Yonhap News Agency reported that relations between North Korea and China have become relatively estranged, in contrast to Pyongyang's growing military and economic cooperation with Moscow amid the ongoing war in Ukraine.

The report also said that expressions emphasizing friendship and cooperation were less frequently used in both Xi's message and Kim's reply than last year.

Attention is focused on whether North Korea will send a delegation to the 75th anniversary of the establishment of diplomatic relations with China on October 6, with Washington as their common adversary in mind.