"The missile launch is an issue that is entirely within our sovereignty. No one has the right to dispute it," Ri Pyong Dok, a researcher on Japanese affairs at the North's Foreign Ministry, said on footage aired by Japanese television network TBS. "On the missile launch, we are not bound by any agreement."

Japanese national broadcaster NHK reported that an unidentified Foreign Ministry official in Pyongyang acknowledged the firing of the missiles, but Ri told reporters that diplomats such as himself are unaware of what the military is doing.

In Russia, Interfax quoted the army chief of staff, Gen. Yuri Baluyevsky as saying the number of missiles fired by North Korea could be higher than the six cited by the US, Japan and South Korea.

"According to various data, 10 missiles were launched. Some say that these were missiles of various classes; however, some claim that all missiles were intercontinental," Baluyevsky was quoted as saying at a news conference in the Russian Far East city of Chita.

In Tokyo, Japanese Foreign Minister Taro Aso warned of a "very high possibility" the UN would level economic sanctions against North Korea. Japan also protested the launches officially through the Chinese capital, and banned a North Korean ferry from Japanese ports for six months.

The tests followed weeks of mounting speculation that North Korea would launch a Taepodong-2. US.intelligence reports indicated Pyongyang was taking steps to prepare for a launch, but the timing was unknown. North Korea refused to confirm the preparations, but insisted it had the right to such a test.

The test was likely to cast a pall over efforts to lure North Korea back to stalled six-party talks on its nuclear weapons program. Pyongyang has boycotted the negotiations to protest a US crackdown on alleged North Korean counterfeiting and other financial crimes. A North Korean official said Wednesday his country would stand by that stance.

Diplomatic moves over North Korea gathered pace. US nuclear envoy Christopher Hill was to leave Washington for the region later on Wednesday, and the launches coincided with a trip by South Korea's security chief to Washington for consultations. China's vice-premier was also scheduled to go to Pyongyang next week.

China urged all parties to remain calm.

"We are seriously concerned with the situation which has already happened," Foreign Ministry spokesman Liu Jianchao said in a brief statement posted on the ministry's Web site.

"We hope that all the relevant sides ... do more things which are conducive to peace and stability ... and not take any actions to escalate and complicate the situation," the statement said.

Two US State Department officials, who spoke on condition of anonymity, said the long-range missile was the Taepodong-2, North Korea's most advanced missile with a range of up to 9,320 miles. Some experts believe it could reach the United States with a light payload.

The missiles all landed hundreds of miles away from Japan and there were no reports the missiles caused damage within Japanese territory, said Japanese spokesman Shinzo Abe.

North Korea's missile program is based on Scud technology provided by the former Soviet Union or Egypt, according to American and South Korean officials. North Korea started its Rodong-1 missile project in the late 1980s and test-fired the missile for the first time in 1993.

North Korea had observed a moratorium on long-range missile launches since 1999.