North Korea said on Tuesday it is ready to launch its controversial long-range rocket on schedule, prompting warnings it could sharply ratchet up tensions on the Korean peninsula.

China reiterated its calls for calm and restraint.

The launch of the Unha-3 rocket, which North Korea says will merely put a weather satellite into orbit, breaches U.N. sanctions imposed to prevent Pyongyang from developing a missile that could carry a nuclear warhead.

...We've already announced that the launch will happen between the 12th and 16th of April and we have already informed international organisations and we will follow the timed schedule, said Ryu Kum-chol, vice director of the space development department of the Korean Central Space Committee.

The launch is due to coincide with the 100th anniversary celebrations of the country's founder, Kim Il-sung. North Korea says that it is its sovereign right to launch the rocket, which it says is for peaceful purposes.

South Korea, which remains technically at war with the North, warned that the impoverished country of 23 million people would deepen its isolation if it went ahead.

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.

Airlines have re-routed flights to avoid the missile's path.

(Reporting by Maxim Duncan; Writing by David Chance; Editing by Nick Macfie)