North Korea has completed all but final preparations for an imminent rocket launch that has been condemned as a covert missile test by its international critics.

A five-day window for the launch opened on Thursday with no signs that blast-off was imminent, but South Korea’s Yonhap news agency reported that the three-stage rocket was standing by, awaiting only final checks and countdown.

North Korea said on Wednesday it had installed the satellite payload and fuelled the 30-metre Unha-3 rocket.

Pyongyang says the rocket is carrying a weather satellite into space and has timed the launch to coincide with national celebrations marking Sunday’s centenary of the birth of its founding leader Kim Il-Sung.

But a government source in Japan told the Kyodo news agency that a launch was not expected on Thursday because of weather conditions.

“The weather is poor, and it is now past the launch time given, so there will probably be no launch,” Kyodo quoted the official as saying.

Weather websites showed that conditions were cloudy over the launch site in northwest North Korea’s Cholsan peninsula.

Full alert

The launch has been condemned by the US and its allies, who say it contravenes UN restrictions on North Korea’s nuclear weapons programme.

Yoshihiko Noda, the Japanese prime minister, said his country was on full alert, while urging North Korea to show “self-restraint until the last minute”.

“But we want to be fully prepared for any possible contingency,” Noda said, after ordering the deployment of anti-missile batteries on land and at sea to shoot down the rocket if it threatens Japanese territory.

The Unha-3 rocket is expected to fly past western Japan, raising concerns that a failed launch, or a falling stage of the rocket, could endanger Japanese lives or property.

A spokesman for South Korea’s defence ministry told reporters: “We’re closely watching developments.”

South Korea has already threatened to deliver a “firm response” to “provocation” if the North goes ahead with the launch.

Elsewhere, at the start of a Group of Eight (G8) meeting in Washington, Hillary Clinton, the US Secretary of State, reiterated that the launch would violate UN security council resolutions.

“North Korea is readying a long-range ballistic missile launch over the East China Sea. It comes just weeks after North Korea agreed to a moratorium on missile testing,” Clinton said, referring to a February deal that would have sent US food aid to the country in return for its halting its nuclear programme.