Chinese President Xi Jinping has extended his congratulations to North Korean leader Kim Jong Un on his new title of chairman of the ruling Workers' Party of Korea.

China's official Xinhua News Agency said Tuesday that Xi, also head of China's ruling Communist Party, expressed hope that Kim's leadership would bring "new accomplishments in the cause of building socialism."

Despite a fraying of ties in recent years, Xi called the traditional friendship between the once-close communist neighbors a "shared treasure."

He said China stood ready to work for further improvements in bilateral relations and to make "positive contributions to safeguarding peace, stability and development in the region."

Kim has yet to visit China, despite its status as the North's key source of economic and diplomatic support.