A defect was found in the H-2A rocket which had been scheduled to lift off at 1:30 pm (0430 GMT) from the southern Japan island of Tanegashima, the National Space Development Agency (NASDA) said.

"Trouble was detected in the second stage of the rocket. The launch will be postponed until October 2 or later," a NASDA official said.

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

The two satellites had been due to join another pair of satellites which were launched 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.

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

The 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 the first pair of satellites, the second set is made of one 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 also enable Japan to photograph North Korea during the afternoon.

These satellites can identify objects as small as one metre (yard) in length, 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 even at night and in cloudy conditions. Researchers expect it will be able to distinguish camouflaged vehicles and facilities.

SPACE.WIRE