"The government is reviewing and will review measures befitting such an incident," he told reporters.

"If North Korea carries out nuclear testing, it would bring about much more grave consequences than its missile launch in July.

"It would create a very serious situation, shaking the global non-proliferation regime to its foundation," Ban said.

South Korea has stepped up monitoring of North Korea's nuclear activities amid news reports that the communist state may be preparing for an underground nuclear bomb test.

The United States and South Korea -- both parties to stalled six-way nuclear disarmament talks with North Korea, along with China, Japan and Russia -- have issued previous warnings to Pyongyang against any nuclear tests.

Ban said South Korea and other parties to the talks were holding close consultations on ways to make a breakthrough in the stalled negotiations.

"Diplomatic efforts are being made to come up with flexible and creative ideas in order to end the current stalemate," he said.

Diplomatic efforts have been intensifying to restart the talks as this issue has taken on greater urgency since North Korea test-fired seven missiles on July 5.

South Korean President Roh Moo-Hyun planned to visit Beijing in October for a summit focusing on North Korea and bilateral economic ties.

If realized, Roh's visit would come on the heels of his summit with US President George W. Bush in Washington on September 14 on a bilateral trade pact and North Korea's nuclear ambitions.

Roh's chief security advisor, Song Min-Soon, is currently in Beijing to seek a breakthrough ahead of US envoy Christopher Hill's reported scheduled visit to East Asia next month.

An imminent test in North Korea was wrongly predicted last year.

But analysts here said the North might pretend to prepare for a nuclear test to push the US into looking afresh at the stalled negotiations.

Japan, along with other countries including South Korea and the US, has been beefing up its monitoring of North Korea's nuclear activities after detecting vehicles entering and leaving a nuclear testing facility, according to Japan's Kyodo news agency.

"We are not sure if the movement is directly leading to an underground nuclear test but we are looking at it (in cooperation) with countries concerned," an unnamed government source was quoted as saying.

The source, however, refused to confirm a South Korean news report that residents of a northeastern region of North Korean had been ordered to evacuate due to fears of radiation.

Related Links
Learn about nuclear weapons doctrine and defense at SpaceWar.com