South Korea's intelligence agency is closely watching relations between North Korea and China, amid increasing signs of the two countries growing apart, officials said Wednesday.

The National Intelligence Service (NIS) said it is monitoring any unusual moves after learning that North Korean leader Kim Jong-un has apparently instructed his diplomats stationed in China "not to mind Beijing" when they are on the job.

South Korea's JoongAng Ilbo newspaper reported earlier in the day that Kim had given the directive to North Korean diplomats in China, quoting unidentified sources.

If true, it would add to the growing speculation that a rift is growing between Pyongyang and Beijing, in contrast to the North's deepening ties with Moscow that became more evident after Russian President Vladimir Putin's visit to Pyongyang last month.

The possibility of Pyongyang and Beijing drifting apart has gained traction after China removed a footprint plaque installed on a road in Dalian in May. The road was where Kim and Chinese leader Xi Jinping had taken a walk together during Kim's visit to Liaoning Province in 2018.

Following a trilateral summit among South Korea, China and Japan in May, North Korea strongly denounced their joint statement, a highly unusual reaction from Pyongyang to the outcome of a diplomatic meeting involving Beijing, its traditional ally and longtime economic benefactor.

Some North Korean defectors have claimed that North Korean authorities began to limit Chinese yuan-based transactions at markets. (Yonhap)