Russian President Vladimir Putin, right, and Chinese President Xi Jinping / EPA-Yonhap

Chinese President Xi Jinping and Russian President Vladimir Putin vowed efforts to advance relations with North Korea in messages sent to leader Kim Jong-un to congratulate him on his country's 73rd founding anniversary Thursday, Pyongyang's state media reported.

"I and Comrade General Secretary have maintained close communication and led the bilateral relations for them to develop in a stable way and, thus steadily made good success, which further enriched the traditional bilateral friendship," Xi was quoted as saying by the Korean Central News Agency.

"I highly value the development of the China-DPRK relations and intend to develop these ties of friendship and cooperation on a long-term basis and in a stable way," he added, using the acronym of the North's official name, the Democratic People's Republic of Korea.