As tensions grew, meanwhile, the U.S. staged war games in the western Pacific on Tuesday with 22,000 troops, 280 aircraft and three aircraft carriers.

U.S. officials have said the missile, believed to be a Taepodong-2, has a firing range of 9,300 miles and could reach as far as the U.S. West Coast. Most analysts, however, say North Korea is still a long way from perfecting technology that would make the missile accurate and capable of carrying a nuclear payload.

The North's missile program has been a major security concern in the region, adding to worries about its pursuit of nuclear bombs. North Korea shocked its neighbors when it test-fired an earlier missile version over northern Japan in 1998.

In Seoul on Tuesday, Woo Sang-ho, a spokesman for South Korea's ruling party, said, "The government explained to North Korea the serious repercussions a missile launch would bring and strongly demanded that test fire plans be scrapped."

The U.S. ambassador to South Korea, Alexander Vershbow, said the U.S. would like to achieve normal relations with the North, saying a missile test "would only further compound North Korea's isolation and put it more apart from the international community."

Japan has said that a new launch would threaten Japanese security and violate an agreement North Korea signed in 2002 and reaffirmed in 2004. Rice said it would also end a self-imposed moratorium on test firings that North Korea has observed since 1999 and a disarmament bargain it struck with the United States and other powers last year.

After its last long-range missile launch in August 1998, the North had said it was seeking to put a satellite in orbit. Pyongyang is widely expected to make a similar claim if it goes ahead with another test launch.

North Korea claims it has nuclear weapons, but isn't believed to have a design that would be small and light enough to top a missile. The North has boycotted international nuclear talks since November over a U.S. crackdown on its alleged illegal financial activity.

Despite the latest standoff, North and South Korea opened two days of meetings in the North Korean border city of Kaesong on Tuesday to work out details over expanding a joint industrial zone there. Some experts believe the South would curtail its economic cooperation with the North in the event of a missile launch.

Former South Korean President Kim Dae-jung is also set to travel to Pyongyang next week to reprise the historic June 2000 summit between leaders from the North and South, although the reports of a possible missile test were complicating the arrangements, one of the former president's aides said Monday.