The United States and Japan urged North Korea not to proceed with reported plans to test-fire a long-range missile that could reach the U.S. mainland, saying Saturday that a launch would be dangerous and provocative.

But North Korean officials later denied such preparations, the Kyodo News agency reported, citing a South Korean official it did not identify.

U.S. Ambassador to Japan Thomas Schieffer and Japanese Foreign Minister Taro Aso met Saturday night amid mounting speculation the North could soon test a Taepodong-2 missile capable of reaching the United States with a light payload.

After the meeting, Schieffer reiterated Washington's stance that the test would be a dangerous act that would hurt North Korean interests. The North has been under a self-imposed moratorium on long-range missile tests since 1999.

"We hope that the North Koreans will not take this provocative action. We hope that they will return to the six-party talks," Schieffer said, referring to international talks aiming to get North Korea to give up its nuclear program.

Those talks — involving the United States, the two Koreas, China, Japan and Russia — have been stalled by a North Korean boycott.

A launch "will only isolate the North Koreans further from the rest of the international community," he said.

Schieffer said Washington was working with allies on how to respond if North Korea goes ahead with the launch, but he refused to be specific, saying only that "all options are on the table."

Japan and the U.S. may seek an immediate reaction from the U.N. Security Council if North Korea fires a long-range missile, Kyodo reported on Sunday.

White House spokeswoman Dana Perino said a North Korean missile launch would violate a moratorium on long-range missile tests declared in 1999 by North Korean leader Kim Jong Il.

"This would be yet another instance of North Korea violating the international commitments it has made," she said.

Aso told reporters that the situation was "serious" and that North Korea had been warned not to fire the missile. "How we will respond depends on what North Korea does," he said.

Japan has grown increasingly tense as news reports emerge that Pyongyang could soon launch the missile. North Korea fired a missile over northern Japan into the Pacific Ocean in 1998, and the move spurred Tokyo to work with Washington on a missile defense system.

A U.S. government official told The Associated Press on Friday that a test of the Taepodong-2 may be imminent. The Washington official agreed to speak but only on the condition of anonymity because of the sensitivity of the information.

South Korean newspaper Chosun Ilbo reported Saturday that North Korea also moved about 10 fuel tanks to the launch site in preparation for the test.

It said intelligence authorities from Seoul and Washington had made the assessment, based on satellite images, that the North had loaded booster rockets onto a launch pad and moved the fuel tanks close by. The paper quoted an unidentified high-level South Korean government official.

Japan's conservative daily Sankei reported that the North Korean government has ordered its people to raise the national flag at 2 p.m. Sunday and to watch a state message on television in the late afternoon.

Sankei, citing government officials it did not name, said the Japanese government had dispatched two Aegis destroyers to the Sea of Japan and the Pacific Ocean. Hidetsugu Iwamasa, a Japanese naval official, said he could not comment on the report, citing security concerns.

North Korea plans to disguise the missile test as an attempt to put a satellite into orbit, Kyodo reported Saturday. Pyongyang has been calculating an orbit for a fake satellite and plans to announce its trajectory after firing the missile, Kyodo reported from Beijing, citing military intelligence officials it did not identify.

North Korea said in 1998 that its launch then was an effort to put a satellite in space, but Washington and Tokyo say that is just a cover for a military program.