WASHINGTON (Reuters) - The missile North Korea is expected to launch as soon as this weekend appears to have a bulb-shaped nose cone consistent with a satellite payload, rather than a warhead, U.S. defence officials said on Tuesday.

A commercial satellite image of the Musudan-ri missile test site showed a Taepodong-2 missile with a bulb-shaped payload cover, said the officials, who spoke on condition of anonymity.

The image was posted March 29 on the Web site of the Institute for Science and International Security, or ISIS, a Washington-based group devoted to informing the public on security issues including nuclear weapons.

The bulb shape is similar to the current nose cone standard for military and commercial satellite launches, concluded officials including analysts at the U.S. Air Force’s National Air and Space Intelligence Centre in Dayton, Ohio.

The same design is used by the United States, Russia, China and the European Space Agency, the analysts said.

North Korea said it will launch a satellite into space April 4-8 and issued a notice to mariners about potentially hazardous conditions in the North Pacific between 3 a.m. and 8 a.m. British time each day beginning on Saturday.

One official said the bulb shape gives credence to North Korea’s contention that it intends to launch a satellite. The nose of a missile with a warhead design would be more likely to be cone-shaped.

North Korea is under mounting international pressure over the launch plan because neighbouring countries and the United States view it as the test of a ballistic missile capable of reaching Hawaii. A Taepodong-2 test in 2006 failed.

The United States, Japan and South Korea are deploying missile-interceptor ships in the area.

“They probably are launching a satellite. But the issue is that the steps they’re going through to do that run parallel to them being able to have other capabilities,” senior ISIS analyst Paul Brannan said.

Brannan said he did not believe the image on the ISIS Web site showed definitively that the missile carries a bulb-shaped payload cover but suggested defence analysts could be comparing it to classified images of far greater clarity.

“The significance of the photo is that it’s the first time you could really see the missile itself. Leading up to then, you couldn’t see it,” Brannan said. “The fact you can see it so clearly on one photo versus the past ones indicated to us that they’d probably been shrouding it.”

U.S. defence officials said a successful satellite launch, expected as early as late Saturday morning in Korea, would bolster Pyongyang’s ballistic missile program.

“It would mean they can use multistage boosters to get a payload to a certain point. That’s half way to bringing a re-entry vehicle back into the atmosphere,” said one official.

Proliferation experts believe the North does not have the technology to miniaturize a nuclear device for a warhead, but might be able to place a biological or dirty bomb in a conventional warhead.

Pyongyang’s only nuclear test in 2006 was seen as a partial success.