Breaking News: North Korea Launches Rocket.

SEOUL, South Korea (CNN) -- North Korea has launched a long-range rocket, a South Korean official confirmed to CNN on Sunday.

The payload of the rocket remains unclear. North Korea has said the rocket was to carry a satellite into space, but the United States, South Korea and other nations fear it could be a missile with a warhead attached.

Earlier Sunday, before the launch, South Korea's national security council called an emergency meeting amid concerns that a North Korean rocket launch was imminent, a presidential spokesperson told CNN Sunday.

On Friday, U.S. President Barack Obama reiterated that the United States strongly opposes any such launch.

UPDATE: SEOUL, South Korea - North Korea launched a rocket that passed over Japan on Sunday, defying calls from world leaders to scrap a plan that has caused international alarm.

The Japanese government said the rocket flew over Japan and its second booster stage had splashed down in the Pacific Ocean, indicating the launch had been successful.

The U.S. State Department confirmed North Korea had launched the rocket but had no further details.

Western aerospace experts said the new North Korean rocket appeared to be fairly large — much bigger than the one Iran fired in February to launch a small satellite, and about the same size as China launched in 1970 in its space debut.

David C. Wright, a senior scientist at the Union of Concerned Scientists, a private group in Cambridge, Mass., said the North Korean rocket might be able to lift a small satellite of 220 pounds into an orbit some 250 miles high. If used as a ballistic missile, he added, the rocket might throw a warhead of 2,200 pounds to a distance of some 3,700 miles — far enough to hit parts of Alaska.

Western analysts agree that North Korea’s missile launching is a military endeavor, despite its payload of an experimental communications satellite and its cocoon of North Korean propaganda. Starting with Sputnik in 1957, most of the world’s intercontinental ballistic missiles began life as satellite launchers.

Dennis C. Blair, the director of national intelligence, told reporters in March that “North Korea is attempting to demonstrate an ICBM capability through a space launch.”

While many analysts have looked at the launching through a military lens, some say another perspective involves political rivalries on the Korean peninsula. For years, South Korea has been gearing up to fire a satellite into orbit and join the space club. Its spaceport of Oinarodo is nearly ready, but a launching scheduled for this month was delayed, giving North Korea an opening.