By Maxim Duncan
PYONGYANG (Reuters) - Isolated and impoverished North Korea said on Tuesday it was ready to go ahead with its proposed long-range rocket launch in a move 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 U.N. sanctions imposed to prevent Pyongyang from developing a missile that could carry a nuclear warhead.
"We are expecting to complete the assembly by today," said Ryu Kum-chol, vice director of the space development department of the Korean Central Space Committee.
"The launch of 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," he added.
The launch, due between Thursday and next Monday, will coincide with the anniversary celebrations of the country's founder and North Korea says that it is its sovereign right to launch the rocket.
The West says it is a disguised ballistic missile test by a country which walked out of so-called six-party disarmament talks three years ago.
South Korea, which remains technically at war with the North after their 1950-53 conflict ended with a truce, not a treaty, warned Pyongyang it would deepen its isolation if it went ahead with the launch.
Security sources in Seoul, citing satellite images, have said that North Korea is also preparing a third nuclear test following the rocket launch, something it did in 2009, a move bound to trigger further condemnation from the West.
"It is disappointing that the North is forcing its people to endure sacrifices with this provocative action and is bringing isolation and sanctions to itself from the international community," the South's Unification Ministry said in a statement.
Russia, a former backer of North Korea which has boosted economic ties with Pyongyang recently, condemned the launch.
"We consider Pyongyang's decision to conduct a launch of a satellite an example of disregard for U.N. Security Council decisions," state-run news agency RIA quoted Russian Foreign Ministry spokesman Alexander Lukashevich as saying.
The rocket will bisect a sea that separates South Korea and China and its flight path will take it towards the Philippines where a second stage of the rocket is due to come down in waters close to the archipelago.
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.
"If North Korea launches a missile, Japan will consider the next step in cooperation with international society including the U.N. Security Council," Japanese Prime Minister Yoshihiko Noda said.
Airlines have re-routed flights to avoid the rocket's path.
News that the launch would proceed on time hit South Korea's financial markets. The 1-month Korean won contract was bid at 1,144 per dollar at 0737 GMT, down from 1,141.8 when the local trade finished at 0600 GMT.
(Additional reporting by Ben Blanchard and Sabrina Mao in BEIJING and Kaori Kaneko in TOKYO; Writing by David Chance; Editing by Nick Macfie)