Preparations for a nuclear test had been completed at North Korea's Punggye-ri test tunnel, where it conducted six underground nuclear tests from 2006 to 2017, the news agency reported, citing legislators briefed by the National Intelligence Service (NIS).

The timing of the test was likely to be determined by events in North Korea's main ally, China, and its biggest rival, the United States, Yonhap reported.

"The NIS said if North Korea conducts a nuclear test, it could be between China's 20th party congress on Oct. 16 and the U.S. midterm elections on Nov. 7," one legislator, Yoo Sang-bum, told the news agency.

(Reporting by Soo-hyang Choi; Editing by Christian Schmollinger)