North Korea's upcoming satellite launch is intended to test a three-stage rocket and develop technology for inter-continental ballistic missiles, an expert said Friday.

A successful launch would mean the communist state has greatly extended the potential range of its missiles, said Sohn Young-Hwan, a missile expert at Technovalue defence technology consulting firm in Seoul.

Pyongyang has told the International Maritime Organisation and the International Civil Aviation Organisation that it will fire a rocket to launch a communications satellite between April 4-8.

It has given locations of possible danger areas which indicate that the rocket's first stage will drop into the sea between Japan and the Korean peninsula and the second stage will plunge into the Pacific.

The coordinates indicate the first stage will fall 650 km (406 miles) east of the Musudan-ri launch site and the second will fall 3,600 km (2,250 miles) east of the site, a Seoul foreign ministry official said.

A third stage may be used to thrust a satellite into orbit, experts said.

"North Korea simply has no practical grounds to have a satellite. It's obvious that it's part of efforts to develop ICBMs," said Sohn.

In terms of the range, it would have "no difference from an ICBM," he told AFP.

"A success would mean the North has developed a launch vehicle for ICBMs. It's quite natural to assume that progress has been made since the 1998 launch," Sohn said.

In 1998 the North fired a Taepodong-1 missile to put a satellite into orbit. The first stage dropped into the sea after 95 seconds.

The second stage flew 1,620 km over Japan before falling into the Pacific, sparking an angry protest from Tokyo.

The third stage sought to place a satellite into orbit but apparently failed.

This time the North is using its longest-range Taepodong-2, whose first test ended in failure in July 2006.

Director of US intelligence Dennis Blair said Tuesday the North is indeed planning a space launch as it claims, but the technology is indistinguishable from intercontinental ballistic missiles.

"And if a three-stage space launch vehicle works, then that could reach not only Alaska, Hawaii but also part of what the Hawaiians call 'the Mainland' and what the Alaskans call 'the Lower 48,'" he said.