China reportedly speculates that an internal political assessment led to North Korea's decision not to conduct a nuclear test around the time of its ruling party congress held early this month.

According to a senior South Korean government official stationed in China who spoke to reporters in Beijing on Thursday, China urged North Korea to refrain from carrying out its fifth nuclear test. The source quoted a senior Chinese official but added that it can't be concluded that Pyongyang stopped short of a test just because of China's request.

The official said that Beijing believes the North must have politically evaluated that a nuclear test will be a minus to the party congress.

The official also said that China also does not know when North Korea may go ahead with another nuclear test but believes the regime is ready to conduct a test any time at leader Kim Jong-un's order, as Kim had publicly declared in March.