US and Japan threaten "appropriate action" if launch goes ahead, as Pyongyang says it has begun fuelling rocket.

Hillary Clinton, the US secretary of state, has urged North Korea not to go ahead with a planned rocket launch if it wants a "peaceful, better future" for its people.

North Korea has so far rebuffed foreign calls to abandon the launch, which it says is to put a satellite into space, and on Wednesday said that it had begun injecting fuel into the rocket prior to a scheduled blast off in the next few days.

"We are consulting closely in capitals and at the United Nations in New York and we will be pursuing appropriate action," Clinton said at a press conference on Tuesday with Koichiro Gemba, Japan's foreign minister, who echoed her remarks.

"If North Korea wants a peaceful, better future for their people, it should not conduct another launch that would be a direct threat to regional security," the chief US diplomat said.

Gemba spoke of US-Japanese cooperation if North Korea goes ahead with the launch of a rocket, which critics say amounts to a disguised missile test by the reclusive nuclear-armed state.

"The United States and Japan would cooperate with each other and the international community, including the Security Council, would take an appropriate measure," Gemba said.

Neither Clinton nor Gemba explained what they meant by "appropriate" action.

The exact date of the launch has not been confirmed by Pyongyang, but it has been scheduled for some time between April 12 and 16 to mark the 100th anniversary of the birth of North Korea's founding leader Kim Il-Sung, a significant date as Kim's youthful grandson Kim Jong-Un cements his own power.

South Korea has already threatened to deliver a "firm response" to "provocation" if the North does goes ahead with its planned launch.

Japan has also braced itself for the launch, having put missile batteries on alert to shoot the rocket down if it passes through Japanese airspace.

The Unha-3 rocket is expected to fly past western Japan, raising concerns that a failed launch, or a falling stage of the rocket, could endanger Japanese lives or property.

"They have come pretty far on the question of range, but they still need a lot to resolve in the precision technology needed for [warhead] re-entry and guidance," a South Korean military official who spoke on condition of anonymity, told the Reuters news agency.

The Unha-3 is believed to be the same three-stage liquid-fuelled ballistic missile the North fired in 2009 over Japan, which eventually splashed down after a 3,800km flight, military experts in South Korea said.

The new rocket is believed to have a design range of more than 6,700 kilometers, and can carry a payload of up to 1,000 kg.

The planned launch has already prompted three Asian airlines to make changes to flight paths to avoid the missile.

Philippine Airlines, Japan Airlines (JAL) and All Nippon Airways (ANA) have announced changes to several routes.

Philippine Airlines said in a statement that as the splashdown area of the rocket's second stage was anticipated to be ''just east of Luzon'', all flights passing through the area during the launch period would have their routes adjusted.

These include about a dozen flights between Manila and the US, Canada, Japan and South Korea.

Philippine officials have also declared a no-fly zone and warned ships and fishing boats to avoid the area where rocket debris could fall.

PHOTO CAPTION

North Korea's Unha-3 rocket, slated for liftoff between April 12-16, stands at Sohae Satellite Station in Tongchang-ri, North Korea on Sunday April 8, 2012.

Al-Jazeera