China's ruling Communist Party has replaced a key official in charge of political relations with North Korea and other countries, according to Chinese state media reports on Thursday.

Wang Jiarui, head of the Chinese Communist Party's international department who held the post for 12 years, stepped down and career diplomat Song Tao was picked as Wang's successor, media reports said.

The website of the department also showed that Song became its head.

It was not immediately known why Wang was replaced.   

A diplomatic source with knowledge of North Korea-China relations said, given the career background of Song, the replacement suggested China's desire to develop state-to-state relations with North Korea.

"Song had never worked for affairs related to the Korean Peninsula," the source said on the condition of anonymity. "Given that he is a career diplomat, the Chinese Communist Party is expected to put more focus on developing a normal and state-to-state relationship with North Korea."

The alliance between North Korea and China has often been described as being "forged in blood" as China fought alongside the North in the 1950-53 Korean War. However, political ties between the allies were strained following North Korea's third nuclear test in early 2013.

Song, 60, was appointed a vice foreign minister in 2011 and served as a minister-level official at the Chinese Communist Party's foreign affairs office.

When Liu Yunshan, the party's fifth-ranked official, visited Pyongyang last month, he was accompanied by Song. (Yonhap)