South Korea said the launch was part of North Korea's annual military exercise. The Office of South Korea's Joint Chiefs of Staff declined to identify the type of the missile, but said North Korea has test-fired the same type of missile two or three times this year.
Japanese Cabinet Office spokesman Yukinori Morita and the Defense Agency said the government had received an unconfirmed report about a land-to-ship missile being fired into the Japan Sea around noon. But they said the information has not been verified. It was the first suspected missile launch by Pyongyang since a test in April.
Meanwhile, Mr. Bush conferred with his South Korean counterpart on Monday on the sidelines of a Pacific Rim summit and claimed progress was being made "on peacefully solving" a crisis with North Korea.
The president and Roh Moo-hyun met over breakfast a day after Mr. Bush rejected North Korea's demand for a formal no-invasion treaty, but left the door open for some form of written security pledge backed by the United States, China, Japan, South Korea and Russia.
Also in Bangkok, Secretary of State Colin Powell accused North Korea of starving its own people as it pursues a misguided nuclear weapons program, but expressed hopes that Washington and the North's neighbors can resolve the crisis diplomatically.
Powell gave no details on how the standoff might end but said "in the course of the next days and weeks we will be flushing out these ideas with our partners…and pursuing them with the North Koreans."
In a speech to business leaders meeting alongside the Asia-Pacific Economic Cooperation summit, Powell poured scorn on Pyongyang's nuclear ambitions.
"You cannot eat plutonium," he said. "You cannot grow a crop because there's a nuclear weapon in a bunker somewhere. It's wasteful of the talent of the North Korean people and what little treasure the North Korean people have."
North Korea says it will give up its nuclear programs only if the United States signs a nonaggression treaty and establishes diplomatic relations.
Powell reiterated Mr. Bush's pledge, made here Sunday, that the United States has no intention of waging war on the reclusive and impoverished North.
"None of us in this conference threatens North Korea," Powell said. "The United States does not threaten North Korea. We have no intention of invading or attacking them."
In August, Beijing hosted multination talks involving North Korea, South Korea, Japan, China, Russia and the United States. But no solution was found. Powell said that he hoped that "in the not too distant future another round will take place."
North Korea said the meeting in Bangkok was not the place to discuss the nuclear standoff because it "is an issue to be resolved between us and the United States."
The nuclear dispute flared a year ago when U.S. officials said North Korea admitted running a secret nuclear program in violation of international agreements. The U.S. cut off fuel shipments and the North kicked out nuclear inspectors.
U.S. intelligence analysts believe North Korea already has at least one or two atomic bombs. Since then, various statements from the North suggest it is building weapons and may test one. The North claims it must defend itself against Washington because of the Bush administration's doctrine of preemptive war.
At the APEC summit itself, the focus was on terrorism. In the summit's draft communiqué, the leaders promise to "dismantle, fully and without delay, transnational terrorist groups that threaten the APEC economies."
The draft communique does not specifically mention North Korea. However, it says leaders want "to eliminate the severe and growing danger posed by the proliferation of weapons of mass destruction" and will clampdown on the trade in these arms.
Security was tight for the summit tight that ends Tuesday. Fighter jets escorted the planes of arriving VIPs and helicopters shadowed motorcades through Bangkok's unusually empty streets.
In other developments:
Japan has grown increasingly wary of the North's arsenal in recent years. Pyongyang is believed to possess missiles that could reach parts of the United States.
But if North Korea did test a missile Monday, it would not have posed any immediate security threat to neighboring countries, a Japan Defense Agency official said on condition of anonymity.
He said the report indicated the missile had a range of about 60 miles. It was believed the firing would have been part of "routine training," he said.
Pyongyang has conducted similar tests of short-range missiles in the past. In 1998, North Korea fired a long-range missile that flew over Japan and plunged into the Pacific Ocean.
North Korea test-fired two short-range missiles in late February and early March amid tensions over its suspected nuclear weapons programs.
In April, U.S. officials said North Korea test-fired an anti-ship missile off its west coast, in an apparent response to the launch by Tokyo of spy satellites to monitor the isolated communist nation days earlier.