North Korea is loading its highly controversial Taepodong-2 missile on its east coast launchpad in anticipation of an early April firing, U.S. officials said Wednesday.

U.S. counterproliferation and intelligence officials have confirmed Japanese news reports of the expected launch between April 4 and 8.

North Korea announced its intention to launch the satellite in February, however, regional powers worry the claim is a cover for the launch of a long-range missile capable of reaching Alaska.

"It is highly likely that the rocket will emerge between March 28 and 31," AFP quotes a South Korean military source, adding it will take more time to add fuel. The source also said South Korea would start a crisis management operation as soon as the rocket is set up.

North Korea faked a satellite launch in 1998 to cloak a missile development test. In 2006, it launched a Taepodong-2 that blew up less than a minute into flight.

Both the satellite launch rocket and long-range missile use similar technology, and arms control experts fear even a satellite launch would be a test toward eventually launching a long-range missile.

South Korea, the U.S. and Japan have urged North Korea to refrain from launching a satellite or missile, calling it a violation of a U.N. Security Council resolution barring the country from ballistic activity and Tokyo media reports say Japan's military may shoot down the rocket if it threatens the country.

South Korea's chief nuclear envoy, Wi Sung-lac, said Wednesday after returning from talks with his Beijing counterparts, that a launch would trigger a response.

"If North Korea launches rocket, certain countermeasures are unavoidable," he said. He refused to elaborate, saying the measures, including any sanctions, would be discussed among U.N. Security Council member nations.

North Korea insists it bears the right to develop its space program and on Tuesday warned the U.S., Japan and its allies not to interfere with the launch.

A 2006 U.N. Security Council resolution prohibits North Korea from engaging in ballistic activity, which Washington and its allies say includes firing a long-range missile or using a rocket to send a satellite into space.

The North warned that any sanctions would violate the spirit of the disarmament-for-aid pact Pyongyang signed in 2007 with five other nations: the U.S., South Korea, China, Japan and Russia.

It probably won't be clear if the latest launch is a satellite or a missile test until footage can be analyzed after the event; the trajectory of a missile is markedly different from that of a satellite.

Analysts have been watching for signs of a satellite or missile on the launchpad in Musudan-ni, the northeast coastal launch site. Satellite imagery from March 16 showed progress toward mounting a rocket, with a crane hovering over the launchpad, said Christian LeMiere, an editor at Jane's Intelligence Review in London.

He said that once mounted, scientists would need at least a week to fuel and carry out tests before any launch. Images from earlier this month did not indicate the rocket or missile had been mounted, he said Wednesday.

The Associated Press and AFP contributed to this report.