Analysts expect North Korea's nuclear test to prompt closer US cooperation with its East Asian allies. South Korea said it would join US-led proliferation drills after long hesitation due to fear of riling Pyongyang.

Defense Secretary Robert Gates will huddle with his South Korean and Japanese counterparts on Saturday at a conference in Singapore, the Pentagon said.

The United States stations a total of around 80,000 troops in Japan and South Korea under security agreements dating back more than half a century.

But Washington's carrot and stick polices have failed to influence North Korea, which also last month fired a long-range missile and bolted a six-nation nuclear disarmament accord.

L. Gordon Flake, who heads the same think-tank, said Washington should not lose sight of its main interest in Northeast Asia - ensuring the region's stability and economic growth.

South Korea said after the nuclear test that it would join the Proliferation Security Initiative drills, despite Pyongyang's warnings that its estranged neighbor's participation would be an act of war.

After North Korea's first nuclear test in 2006, some hawkish members of Japan's ruling Liberal Democratic Party called for studies on whether the officially pacifist nation should develop nuclear weapons.

While the idea never gained traction, serious talk of going nuclear had long been unthinkable in Japan, the only nation to have suffered nuclear attack.

This time around, some Liberal Democrats have called for Japan to acquire the capability to carry out pre-emptive strikes that could eliminate North Korean missiles.

Experts said Mr Obama would need to balance Japan's desires for robust action with the more cautious approach of China, which is seen as having the most influence of North Korea but dreads an implosion of its impoverished neighbor. -- AFP