North Korea's disastrous bid to launch a Taepodong-2 missile showed Pyongyang has a long way to go before mastering long-range ballistic technology and has failed to draw lessons from previous botched attempts, experts told AFP Friday.

-- What did North Korea launch?

Pyongyang said it fired a Unha-3 rocket to place a scientific satellite into orbit. The US military said North Korea launched a ballistic intercontinental missile (ICBM), a Taepodong-2, which could be outfitted with a nuclear warhead.

The Taepodong-2, which is about 30 meters long, has three stages with a range of 6,000 to 9,000 kilometers, according to most estimates. North Korea already tested the missile in July 2006 and April 2009, and the regime launched a Taepodong-1 in 1998. All three previous tests ended in failure as well.

-- What happened?

The missile lifted off at 7:38 am (2238 GMT) from the northwest base of Tongchang-ri and exploded in mid-air at 7:41 am after traveling in a southerly direction, according to the South Korean defense ministry.

The first stage of the rocket separated and fell into the Yellow Sea about 165 kilometers west of Seoul. But the second and third stages failed, US and South Korean officials said.

The missile exploded at an altitude of 70.5 kilometers, with two pieces of the rocket continuing to ascend to 151.4 kilometers before the debris fell into the sea.

-- What caused the failure?

It is too early to say definitely what caused the unsuccessful launch but "it seems it could have been a problem with the second stage separating and firing," said Peter Crail, an analyst with the Arms Control Association. "The first stage landed somewhere where North Korea had planned."

The result represented a "step backward" for Pyongyang, as the first and second stage had separated successfully in two previous tests, he said.

Managing the separation of stages in a rocket launch is a tough technical challenge that countries with more advanced missile programs still struggle with, said Hans Kristensen, of the Federation of American Scientists.

"If a separation for example happens too late, or not at all, then you can have a second stage igniting -- still being attached to the lower part, and it will blow the thing to pieces," he said.

The timing for each stage has to be exact, and too much vibration could also derail the separation, he said.

-- What does the failure show about Pyongyang's missile program?

The result suggests the regime's effort is "a bit erratic" and that "they seem to have programmatic problems in terms of learning from their mistakes and successes and then building upon that," Crail said.

In the 2006 test, the second stage was based on a Soviet Nodong missile while in 2009 and in the latest attempt the second stage was modeled after a more modern Russian SSN-6.

The failed test indicates North Korea "has not yet overcome industrial processes such as quality control, reliability analysis, systems integration and technologies like propulsion and altitude control," said Poornima Subramaniam, an analyst at the leading defense journal IHS Jane's.

-- What is North Korea trying to achieve with its missile project?

A ballistic missile program requires several years of successful tests to be credible, experts said. In 14 years, North Korea staged four tests -- all ending in failure.

"We're still looking at several years off before the North Koreans have a reliable ICBM," said Crail, adding it would take at least another two to three years.

It may be the regime is not looking to build a reliable program, but merely one that poses a potential threat, he said.

"They want to show that they can possibly reach the United States. Simply having a successful test sometime may be good enough to establish what they can call a deterrent," he said.

North Korea was a long way from entering the "league" of states with long-range missiles armed with atomic warheads, Kristensen said. "If North Korea is going to get some form of deliverable nuclear capability, it's not going to happen right away."