LATEST: NORTH Korea appears to be preparing a fourth nuclear test, but South Korean officials have played down earlier reports the tests were imminent.

A top South Korean official says he misspoke in mentioning "indication" of North Korea nuclear-site work following reports reports of stepped up activity at its main atomic test site.

Earlier, Ryoo Kihl-Jae told a parliamentary committee hearing there were "signs" of an upcoming nuclear test.

A South Korean government source had earlier tipped off the Joong Ang Daily newpaper that the North was preparing the site.



This comes on the heels of the South’s defence ministry reports that Pyongyang could perform a mid-range missile test-launch by Wednesday – also the deadline it has given to foreign diplomats to evacuate, as their safety would reportedly no longer be guaranteed by the government.

“We have detected increased activity of labor forces and vehicles at the southern tunnel of the test site in Punggye-ri, where the regime has worked on maintenance for facilities since its third nuclear test in February,” a high-ranking South Korean government official said.

“The activities appear to be similar to those before the third test, so we are closely monitoring the site."

Japan will shoot down any missile

Meanwhile, Japan has ordered its armed forces to shoot down any North Korean missile headed towards its territory, a defence ministry spokesman said Monday as speculation grows Pyongyang may fire one this week.

Defence Minister Itsunori Onodera issued the order, which will see Aegis destroyers equipped with sea-based interceptor missiles deployed in the Sea of Japan, the defence official said.

The official, who was speaking on condition of anonymity, said the order, which was issued Sunday, was routine and was being kept low-key.

"We won't hold press conferences on this order because of Japan's policy principle that we will not be swayed by North Korean provocations.

"If we announce this publicly and explain in details, North Korea will get to know part of our strategy,'' the spokesman told AFP.

Test-launch of missile 'by Wednesday'

Earlier, a top South Korean security official says North Korea may test-launch a missile this week, as the United States delayed its own missile test due to soaring tensions on the peninsula.

Kim Jang-Soo, chief national security adviser to President Park Geun-Hye, said a test-launch or other provocation could come before or after Wednesday, the date by which the North has suggested that diplomats leave Pyongyang.

North Korea, incensed by UN sanctions following its nuclear and missile tests and by South Korean-US military drills, has issued a series of apocalyptic threats of nuclear war in recent weeks.

It has also reportedly loaded two medium-range missiles on mobile launchers and hidden them in underground facilities near its east coast, raising speculation it is preparing for a provocative launch.

"There are no signs of a full-scale war as of now, but the North will have to prepare for retaliation in case of any local war,'' said Kim.

The spate of threats was intended to force the South and the United States to reach out with face-saving concessions, he said.

Diplomats fear the rhetoric has created a situation which could spiral out of control, and the US delayed an intercontinental ballistic missile test to avoid stoking tensions with the North.

A US defence official said Defence Secretary Chuck Hagel postponed the Minuteman 3 test at Vandenberg Air Force Base until next month due to concerns it "might be misconstrued by some as suggesting that we were intending to exacerbate the current crisis with North Korea''.

And South Korea and the US postponed a major military meeting due to take place in Washington, Seoul's military said Sunday, reportedly due to fear of a provocation while Seoul's military chief is away.

Pyongyang tells diplomats: We can't guarantee your safety

Diplomats in Pyongyang huddled at the weekend to discuss a warning from the North's authorities that their safety could not be guaranteed after April 10 if a conflict broke out.

Most of their governments have made it clear they have no immediate plans to withdraw personnel, and some suggested the advisory was a ruse to fuel growing global anxiety over the crisis.

German Foreign Minister Guido Westerwelle reiterated that "any deadline after which North Korea would no longer ensure the security of embassies is unacceptable'', his ministry said.

British Foreign Secretary William Hague said he saw no immediate need to withdraw his country's diplomats.

Hague also told the BBC the North is showing no sign of gearing up for "all-out conflict'' by repositioning its armed forces, and called for calm.

He said there was a "danger of miscalculation by the North Korean regime which has worked itself up into this frenetic state of rhetoric in recent weeks and the danger that they would believe their own paranoid rhetoric''.

"But it's also important to stress that the international response to this, including our response, must be clear, united and calm,'' Hague added.

China is the North's sole major ally but its patience with Pyongyang also shows signs of wearing thin.

Foreign Minister Wang Yi said China opposes"provocative words and actions'' from any party in the region and would ``not allow troublemaking on China's doorstep'', in sharply worded comments to UN chief Ban Ki-moon.

Beijing said it had asked the North to ensure the safety of its diplomats.

China 'must do more' to rein-in North

But US senior Republican senator John McCain on Sunday criticised China for not doing enough to keep North Korea in check.

"China does hold the key to this problem. China can cut off their economy if they want to. Chinese behaviour has been very disappointing,'' he said, speaking on CBS's Face the Nation talk show.

The North's mobilised missiles are reported to be untested Musudan models which are believed to have a range of around 3000km that could theoretically be pushed to 4000km with a light payload.

The North has no proven inter-continental ballistic missile capability that would enable it to strike more distant US targets, and many experts say it is unlikely it can even mount a nuclear warhead on a mid-range missile.