SEOUL • North Korea, with an eye on conducting more tests of atomic devices in the future, is digging a new tunnel at its nuclear test site, a South Korean news report said yesterday, two days before the leaders of South Korea, Japan and China are to meet in Seoul.

United States Defence Secretary Ashton Carter will make a separate visit tomorrow to discuss with South Korean defence officials how to respond to the North's missile and nuclear threat.

The site is on North Korea's east coast, where three previous nuclear tests were conducted, and there is an active movement of workers and vehicles working on a new tunnel, Yonhap news agency quoted an unnamed government source as saying. "The fact that they are constructing a new tunnel indicates the intention is to conduct a nuclear test at some point," the source said.

There was no evidence to conclude the preparation was for an imminent test, the source added.

South Korea's Unification Ministry spokesman Jeong Joon Hee declined to confirm the report, but said the country and the US are closely watching for any nuclear activity by the North.

The report comes as the leaders of South Korea, Japan and China are scheduled to meet in Seoul tomorrow, where reining in the North's pursuit of weapons of mass destruction is likely to be discussed.

North Korea has been steadily working on its nuclear programme, but a fourth nuclear test was not seen as imminent, particularly after it agreed with the South in August to work towards easing tensions on the peninsula. The most recent test was conducted in 2013.

REUTERS