PYONGYANG - Isolated and impoverished North Korea said on Tuesday it was ready to go ahead with its proposed long-range rocket launch, an announcement that sparked immediate condemnation from South Korea and Russia and a plea from China, its main ally, for calm. The launch of the Unha-3 rocket, which North Korea says will merely put a weather satellite into space, breaches UN sanctions imposed to prevent Pyongyang from developing a missile that could carry a nuclear warhead. Russia, a former backer of North Korea which has boosted economic ties with Pyongyang, denounced the program. "We consider Pyongyang's decision to conduct a launch of a satellite an example of disregard for UN Security Council decisions," state-run news agency RIA quoted Russian Foreign Ministry spokesman Alexander Lukashevich as saying. North Korea defended the launch as a sovereign right. "The weight of our satellite is 100 kg. If it was a weapon, a 100 kg 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. Ryu said that the rocket assembly would be complete on Tuesday. 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, whose grandson, Kim Jong-un, now rules. Kim Il-sung died in 1994. "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," Ryu added.