Japan plans to send two more spy satellites into orbit by March 31, 2007, to strengthen the monitoring of movements in North Korea, notably its missile and nuclear development facilities, according to government sources.

If successful, Japan will have a total of four spy satellites in operation, together capable of taking a photo of any ground spot in North Korea once a day, up from the current once every two days.

Two spy satellites were placed in orbit with the domestically developed H-IIA rocket for the first time in March 2003.

But H-IIA launches had been put on hold following a humiliating failure minutes after liftoff in November 2003. Controllers had to detonate that rocket and its payload of two spy satellites in midair after a booster failed to detach.

After redesigning its booster -- the cause of the unsuccessful launch -- the rocket successfully placed a multipurpose weather and navigation satellite into orbit last February.

The government earlier planned to launch the two additional satellites during fiscal 2005 through this March but postponed it to the coming fiscal year after finding defects in the satellites.

Japan's spy satellite system consists of a pair of devices -- one equipped with an optical sensor and the other with a synthetic aperture radar.

The optical satellite is reportedly capable of resolving an object of 1 meter and of distinguishing such objects as a car on the ground. The radar satellite is believed to be able to observe in the dark and through clouds, at a resolution of 1 by 3 meters.

About 61 billion yen has been earmarked for the launch and operation of spy satellites in the 79 trillion yen budget for fiscal 2006.

The government calls the devices "information-gathering satellites" because they are also used to monitor developments in the event of natural disasters.

Japan is currently developing a next-generation spy satellite whose image-resolution capacity is higher than the existing one and plans to launch a third set of satellites in fiscal 2009.

But even the next-generation satellite, which is expected to be capable of distinguishing an object 50 cm in length, is still far inferior to U.S. spy satellites.

"It can manage to compete with commercial satellites of the United States," said an official at the Cabinet Secretariat, which manages the spy satellites.

A fourth set of satellites with much greater distinguishing capabilities are to be launched in fiscal 2011 or later, the government sources said.

The government decided to launch spy satellites after North Korea fired a long-range Taepodong ballistic missile over Japan into the Pacific in 1998.

North Korea says it was a multistage rocket for sending a satellite into orbit.