Japan has dispatched ships and planes to monitor North Korea amid concerns it is preparing to test-fire a long range missile.

Fukushiro Nukaga, the head of Japan's Defense Agency, confirmed Thursday, that Tokyo is conducting its own surveillance of developments in North Korea.

Recent satellite images indicate North Korea appears to be getting ready to launch a missile capable of reaching the United States.

Japan's senior vice foreign minister says Japan currently has no information indicating Pyongyang has the technology to minimize the size of a nuclear warhead to load it onto a missile. He said a high level of technology is needed for the procedure.

China, meanwhile, said it is "very concerned" about a potential missile test by North Korea and urged greater action by all parties to resolve the issue.

The U.S. ambassador to the United Nations, John Bolton, says the launch of a missile by Pyongyang, particularly if it goes over Japanese territory, is something Washington cannot accept.

North Korea's last test of a long-range missile crossed over Japan and landed in the Pacific ocean in 1998.

The reclusive communist state announced last year it had developed nuclear weapons, but has maintained a self-imposed test ban since 1999.

The U.S. has rejected an offer from a North Korean diplomat for direct talks with Pyongyang on the missile issue. U.S. officials say any dialogue with Pyongyang must come in the context of six-party nuclear disarmament talks that have been stalled since November.

Some information for this report was provided by AFP, AP and Reuters.