North Korea's Musudan or Hwasong-10 intermediate-range ballistic missile put in an impressive performance in its sixth test after five failures, but the missile is far from a reliable weapon, a top U.S. missile expert said Thursday.

John Schilling, an aerospace engineer with expertise in North Korea's missile program, warned, however, that the North's experiment with the Musudan missile could help its intercontinental ballistic missiles, such as the KN-08 and KN-14, reach operational status earlier than expected.

"The Musudan is not a reliable weapon, and Pyongyang does not seem to be trying to make it a reliable weapon," Schilling said in an article to the 38 North website.

"But even if this is just a propaganda stunt and the Musudan is to be quietly abandoned, this partial success increases the likelihood that North Korea's KN-08 and KN-14 road-mobile inter-continental ballistic missiles will reach operational status early in the next decade," he said.

The North fired two Musudan missiles off its east coast early Wednesday in its fifth and sixth attempt to test the missile. The first one exploded in mid-air, but the second missile flew about 400 kilometers before landing in the East Sea in an indication of progress. All four previous tests that began two months ago ended in failure, with the missile either exploding or crashing shortly after launch.

On Thursday, the North's official Korean Central News Agency said that the latest test of what it calls the Hwasong-10 medium-range strategic ballistic missile, known as Musudan in the outside world, was successfully carried out with leader Kim Jong-un in attendance.

The KCNA said the missile flew out of the atmosphere as it soared to an altitude of 1,413.6 kilometers before successfully re-entering the atmosphere and landing in targeted waters about 400 kilometers away.

If confirmed, the launch would mark important progress in the North's missile program as re-entry technology has been considered one of the hardest obstacles the North must overcome before developing a nuclear-tipped intercontinental ballistic missile. Schilling said, however, that it is difficult to view the test more than a partial success.

"As a test, this isn't as useful as launching the missile on its more usual ballistic arc. It gives the engines a full workout, but makes it harder to verify the performance of the guidance system. It also provides a different reentry environment, and testing the reentry vehicle is going to be critical to North Korea," he said.

Schilling said the test could have been little more than a "propaganda stunt," pointing out that the sixth test came just a few hours after the fifth test failed.

"There is no possibility, in that timeframe, of figuring out what went wrong with the first missile and fixing it. As with the earlier Musudan tests, this isn't so much an engineering program so much as an exercise in tossing a coin or rolling a die until it comes up with the result they like," he said.

"We should probably assume they don't really care, that this was about propaganda and image rather than engineering and weapons development. They have achieved something that is as close to a win as possible without overflying Japan, and if they try again there's a good chance that Musudan #7 will be an embarrassing failure just like Musudan #5," he said. (Yonhap)