A U.S. official said on Saturday that North Korea’s new intercontinental ballistic missile broke up upon re-entry at the end of its test launch last week, indicating that North Korea still lacks the key component of reliable heat shielding for its ICBMs.

“The North Koreans had problems with reentry,” said the official, as quoted by CNN.

“Coupled with the rogue regime’s need to master missile guidance and targeting, the re-entry failure underscores the challenges facing the country’s weapons program, according to the official. Still, the ability of the new missile to fly higher and longer than others in the past signals the program’s intent to develop weapons capable of attacking the U.S.,” CNN added.

U.S. and allied ships are reportedly still searching for debris from the missile, which came down near the coast of Japan. Careful analysis of recovered debris could provide further clues to the weapon’s capabilities.

There is still some debate about whether the new missile represents a truly new classification of vehicle, as North Korea insists, or if it would be better viewed as an incremental upgrade over the Hwasong-14. Most media outlets have adopted North Korea’s preferred “Hwasong-15” designation for the system, noting that it’s definitely much larger and seems capable of significantly longer flight times than its predecessor.

Another important attribute of the new system noted by CNN is that it appears to use liquid fuel for at least some of its engines. A fully solid-fueled missile would be much faster to launch and harder for outside observers to detect.

The crew of a Cathay Pacific airplane flying from San Francisco to Hong Kong reported seeing the North Korean missile “blow up and fall apart” at the end of its test flight. Two South Korean planes also reported witnessing the missile test. The threat posed by North Korea’s sudden missile launches to civilian aviation is a growing concern in the region, although experts rate the probability of midair collisions as very low.

The Japanese Parliament declared on Monday that North Korean missile tests are an “unprecedented, significant, and imminent threat” and adopted a resolution condemning last week’s launch.

“This is a frontal challenge against the international community that must not be tolerated,” the resolution said.