WASHINGTON - North Korea has placed a long-range missile on a launch pad, a US official said Wednesday, drawing a US warning that it would take the matter to the United Nations if Pyongyang goes forward with a launch.

US Secretary of State Hillary Clinton said a launch for any purpose would be a "provocative act" in violation of a UN Security Council resolution.

"We intend to raise this violation of the UN Security Council resolution, if it goes forward, in the UN," Clinton said during a visit to Mexico City.

The official said the missile was believed to be a Taepo-dong 2, a long range missile that could, in theory, reach Alaska.

NBC News, citing US officials, said two stages of the missile were visible but that the top was covered with a shroud supported by a crane.

North Korea has said it intends to launch a satellite over Japan and into orbit between April 4 and April 8.

The United States, South Korea and Japan suspect, however, that the planned launch is a disguise for a missile test.

On Tuesday, North Korea warned that stalled six-party nuclear disarmament talks would collapse if new UN sanctions are imposed to punish the launch. The forum groups the United States, Japan, Russia, the two Koreas and China.

Japan's security council, meanwhile, will meet this week to prepare for the shooting down of a North Korean rocket if it threatens to hit the country, Prime Minister Taro Aso said Wednesday.

Japan's government will issue an advance order Friday for the Self-Defense Forces to use its Patriot missile defense system to destroy any missile or debris if it shows signs of falling toward Japan, Jiji Press reported.

North Korea says it would regard a rocket intercept as an act of war.

The last time North Korea launched a Taepo-dong 2, on July 4, 2006, the missile failed catastrophically seconds after launch. Success this time would show that it is capable of reaching Alaska or Hawaii with a nuclear capable missile.

Admiral Timothy Keating, the US commander in the Pacific, said earlier this month there was a "high probability" that the United States could intercept a missile aimed at its territory.

Washington and Tokyo have worked jointly on a missile defense shield, using land and sea-based missiles, against a possible attack from North Korea, which fired a missile over Japan in 1998 and tested a nuclear bomb in 2006.

Pyongyang has said that the rocket's first booster will likely plunge into the Sea of Japan (East Sea) off Japan's northern Akita prefecture, while the second will drop into the Pacific between Japan and Hawaii.

The Sankei Shimbun said in an unsourced online report that "North Korea has entered into the final stage of preparing for a launch as it has moved a rocket from storage."

The Mainichi Shimbun said in an online report, quoting an unnamed South Korean defense source, that the missile was in place and would in theory be ready for launch as early as Saturday.

In addition to the impending missile launch, tensions have been rising between North and South Korea. The North in January scrapped all peace pacts with its neighbour.

China's military chief, General Chen Bingde, arrived Wednesday in Seoul for talks with senior South Korean officials amid rising tensions over North Korea's planned rocket launch.

China, a traditional ally and major aid donor for impoverished North Korea as well as a permanent UN Security Council member, has not publicly urged Pyongyang to halt the launch.

Japan's Foreign Minister Hirofumi Nakasone on Tuesday admitted the difficulty of shooting down a flying missile, particularly when it comes unannounced.

"I guess it is true that it is difficult," he told reporters.

"Our country has never really intercepted a missile. We would not know in what way, how, and to where a missile would be headed.

"What's important, I think, is that we do our best until the very last minute so that it would not happen," Nakasone said.