MODERNISING ARSENAL

White House spokesman Tony Snow on CBS television show "Face the Nation," reminded viewers that in 1999 North Korea declared a moratorium on missile testing and had signed a memorandum in September 2005, which committed it to pursuing peace and security within the region.

"We certainly hope they're going to continue to abide by their agreement," Snow said.

Japanese Foreign Minister Taro Aso said in a television interview his country would seek an immediate meeting of the U.N. Security Council if Pyongyang went ahead with a test.

He voiced concern about the possibility of a missile landing on Japan, but toned down a remark made in an earlier interview that Japan would automatically regard this as an attack.

"We will not right away view it as a military act," he said.

Aso stopped short of saying what Japan and the United States would do in the event of a launch.

But he said: "The responses will be rather harsh."

Reports of test preparations come as six-country talks on Pyongyang's nuclear programs are locked in a stalemate and attention has shifted to concerns about Iran's atomic ambitions.

Many experts have said North Korea has missiles that can hit all of South Korea and probably all of Japan. 

A launch would almost certainly involve a Taepodong-2 missile with an estimated range of 3,500 to 4,300 km (2,175 to 2,670 miles), U.S. officials have said, putting parts of Alaska within reach.

North Korea shocked the world in 1998 when it fired a Taepodong-1 missile, part of which flew over Japan and landed in the Pacific Ocean.