North Korea has said that it is ready to go ahead with its proposed long-range rocket launch.

However, the announcement has led to immediate condemnation from South Korea and Russia and a plea from China for calm.

North Korea says the launch of the Unha-3 rocket will merely put a weather satellite into space.

However, South Korea says it breaches UN sanctions imposed to prevent the North from developing a missile that could carry a nuclear warhead.

Russia, a former backer of North Korea which has boosted economic ties with Pyongyang, has denounced the programme.

"We consider Pyongyang's decision to conduct a launch of a satellite an example of disregard for UN Security Council decisions," said Russian Foreign Ministry spokesman Alexander Lukashevich.

North Korea defended the rocket launch as a sovereign right.

"The weight of our satellite is 100kg. If it was a weapon, a 100kg payload wouldn't have much of an effect. Our launching tower is built on an open site," said Ryu Kum-chol, vice director of the space development department of the Korean Central Space Committee.

Mr Ryu said that the rocket assembly would be complete sometime today.

The launch is set to take place between Thursday and next Monday around the 100th birthday celebrations of the founder of North Korea, Kim Il-Sung.

"The launch of the Kwangmyongsong-3 satellite is the gift from our people to our great leader, comrade Kim Il-sung, on the occasion of his 100th birthday, so this cannot be a missile test," Mr Ryu added.

The West says the launch is a disguised ballistic missile test by a country that walked out of six-party disarmament talks three years ago.

South Korea has warned the North that it would deepen its isolation if it went ahead with the launch.

China, which backs North Korea economically and diplomatically, reiterated its pleas for calm and said it had "repeatedly expressed its concern and anxiety about the developments", Foreign Ministry spokesman Liu Weimin told a press briefing in Beijing.

The prospect of a North Korean rocket launch has alarmed Japan, which was overflown by an earlier rocket and said it would shoot it down if it crossed its airspace.

British Prime Minister David Cameron said in Tokyo he would discuss North Korea with Japanese Prime Minister Yoshihiko Noda.

Airlines, including South Korea's Korean Air Lines, Philippine Airlines and Cebu Air, have re-routed flights to avoid the rocket's path.