Trouble occurred at the last minute in the H-2A rocket which had been scheduled to lift off with the satellites at around 1:30 pm (0430 GMT) from the southern Japan island of Tanegashima, the National Space Development Agency (NASDA) said.

The two satellites are due to join another pair of satellites which were sent into orbit on March 28, in a 250 billion yen (2.2 billion dollar) government project to put four spy satellites into full operation this year.

A glitch was found in equipment that controls the positioning of the rocket's second stage, a NASDA official said.

"There was abnormal reading of data in the equipment and we determined after a check-up that it was defective," he said. "We decided on the postponement just before one o'clock."

He added that the launch would be made on Thursday or later due to the time required for displacement of fuel and inspections.

Some 400 police and coastguard officials have been guarding the launch site on the tiny island off the southern tip of Kyushu Island.

The launch, originally set for September 10, had already been delayed twice by prolonged preparations and replacement of parts.

North Korea denounced the deployment of the first two satellites as a "hostile act" which could trigger a renewed arms race.

The satellite project is intended as a response to North Korea's firing of a suspected Taepodong ballistic missile over Japan and into the Pacific in August 1998, a move which sent shockwaves around the region.

As with the first pair of satellites, the second set has one equipped with optical sensors and another with all-weather radar-imaging capabilities.

The first two satellites pass over North Korea twice a day, in the morning and at night. The two new satellites will enable Japan to photograph North Korea during the afternoon.

The satellites can identify objects as small as one metre (yard) long, matching the technology of current commercial imaging satellites, but they are not as good as US military satellite hardware.

The radar-imaging satellite can take pictures at night and in cloudy conditions. Researchers expect it will be able to distinguish camouflaged vehicles and facilities.

The postponement augured ill for the start of Japan's new space administration.

Under government reforms, NASDA is scheduled to merge on Wednesday with the Institute of Space and Astronautical Science while the National Aerospace Laboratory of Japan will merge with the Japan Aerospace Exploration Agency.

SPACE.WIRE