China has used diplomats to warn North Korea against pushing through with its fourth nuclear test, several diplomatic sources in China said.

The warning comes in the wake of NoKor's new threats of "countermeasures" against the US.

The United Nations (UN) has imposed heavy sanctions on North Korea starting 2006 but the latter has refused to abandon its nuclear ambitions. Its latest nuclear test was launched in February 2013, Reuters detailed.

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A Western diplomat briefed by Chinese authorities said China has encouraged North Korea not to proceed with another nuclear test. Other sources said China has utilized diplomats in Beijing and Pyongyang to communicate its disapproval of the fourth test.

China is currently the most important economic and diplomatic ally of North Korea. For this reason, the US has encouraged China to use its ties with NoKor to convince the latter to stop its nuclear weapons program.

Meanwhile, China has repeatedly called on all involved parties to take it easy on the Korean peninsula, without specifically mentioning North Korea.

China has agreed with the stricter UN sanctions after NoKor launched its third test last year. However, Beijing has been criticized by western nations and other experts for not implementing the sanctions properly.

The Chinese government fears that NoKor's nuclear ambitions will cause instability to occur in the region. According to Foreign Minister Wang Yi, stripping the peninsula of nuclear arms was the only way to achieve peace.

On Monday, Japan announced that it is set to meet with North Korea next week to discuss several issues including Pyongyang's nuclear programs. The talks will be held in Stockholm from May 26 to 28. Similar high-level talks have been held in Beijing in late March.

China-based North Korea expert Zhang Liangui said China would most likely support another set of tougher sanctions should NoKor proceed with another nuclear test.