The Democratic People's Republic of Korea (DPRK) has begun fuelling a long-range rocket it plans to launch between April 4-8, CNN said, starting a process that experts say means the rocket will be ready for lift-off in three to four days.

This DigitalGlobe's QuickBird satellite image taken on March 29, 2009 shows the North Korea rocket launch facility in Musudan Ri, DPRK. [Chinadaily.com.cn via agencies]

The US news broadcaster quoted a senior US military official as saying the DPRK had begun fuelling the long-range rocket and it could be ready for launch by the weekend, according to a report on its website seen in Seoul on Thursday.

North Korea has said it is putting a satellite into orbit as part of its peaceful space program.

The launch will be the first big challenge for US President Barack Obama in dealing with the DPRK.

In London on Wednesday, a US official, speaking on condition of anonymity on the sidelines of a G20 meeting, said Washington would respond to any DPRK launch by raising the matter in the UN Security Council.

"The president made clear we are deeply concerned about the prospective missile launch by the North Koreans ... There will be a reaction to it," the official said.

Several missile-interceptor ships with sophisticated radar from Japan, the United States and South Korea are expected to be in waters along the rocket's flight path but there are no plans to intercept it unless it threatens their territories.

The DPRK criticized on Tuesday Japan's warning it will destroy debris from its rocket launch, and issued a warning of its own.

"Should Japan dare recklessly intercept the DPRK's satellite, its army will consider this as the start of Japan's war of re-invasion more than six decades after the Second World War and mercilessly destroy all its interceptor means and citadels with the most powerful military means," the official KCNA news agency said in an article.

(Xinhua News Agency via agencies April 2, 2009)