South Korea has accused the communist North of preparing to defy the world yet again by readying for the launch of an intercontinental ballistic missile.

Satellite photos reportedly show North Korea moving a long-range missile towards its launch site on the east coast, with experts saying it could be ready for launch within a fortnight.

But over the weekend US Defence Secretary Robert Gates warned that the United States would not stand idly by as Pyongyang develops nuclear weapons.

In its latest belligerent bulletin, North Korean state TV warned the world yet again that any fresh United Nations Security Council sanctions would be met with what it called 'self-defence measures'.

One so-called self-defence measure, the alleged intercontinental ballistic missile, could already be on its way to a launch site at Musundan-ri in the Stalinist state's north-east.

Last week the communist North conducted a nuclear test and followed that over several days by firing short-range missiles.

At a meeting of Asian defence ministers in Singapore over the weekend, Mr Gates offered an assurance to North Korea's jittery neighbours.

"We will not accept North Korea as a nuclear weapons state. We will not stand idly by as North Korea builds the capability to wreak destruction on any target in the region or on us," he said.

As Mr Gates was speaking, the first deployment of American F-22 Raptor fighter jets was landing on Okinawa in southern Japan.

This mission was authorised before North Korea detonated its nuclear device last week, but in a phone call to Japanese Prime Minister Taro Aso, US President Barack Obama said the arrival of the stealth fighters reinforced the US commitment to Japan.

Pyongyang knows that US warplanes based in Japan can be in North Korean air space within 30 minutes.

Washington knows that Pyongyang has 1.2 million fully trained troops and an arsenal of rockets pointed at Seoul and Tokyo.

For Japan, the most immediate priority is the UN Security Council finalising a new resolution with tougher sanctions on the Stalinist state.

Speaking in Singapore Japanese defence minister Yasukazu Hamada urged the Security Council to take a hard line against North Korea.

Just how hard that line will be should be known within days. By that time it should also be known whether North Korea is readying another long-range missile for launch.