North Korea has yet to master reentry technology and overcome other challenges if it wants to use its recently tested long-range rocket as an intercontinental ballistic missile, a U.S. expert said Tuesday.

John Schilling, a U.S. aerospace engineer with expertise on North Korean rockets, also said in an article carried by the website 38 North that the communist nation would need as least one more test launch to overcome such challenges.

"The obvious concern is that North Korea is testing ballistic missiles and only pretending to care about satellites," Schilling said, adding that the North's Unha-3 rocket tested in late 2012 and the latest rocket launched on Sunday "could certainly be used as an ICBM."

Even if the North has mastered the technology to make nuclear warheads small enough to fit on the rocket, it should test a "reentry vehicle that would survive hitting the atmosphere at roughly 16,000 miles per hour," the expert said.

"That's not an insurmountable technical challenge, and we expect North Korea will succeed when it gets around to it," he said.

The North should also work on the rocket guidance system to improve accuracy, he said.

Even if all such challenges are resolved, the North's rocket is still too big, weighing almost 100 tons, and can "only be launched from fixed sites and requires so much preparation that we can see it being readied days before launch," Schilling said.

"That doesn't make for a useful weapon," he said.

The North could try to overcome the handicap by building hardened silos.

"Should anyone find silos set up to hold Unha-sized rockets, any pretense that this is just a satellite program would vanish and we would know that North Korea is deploying ICBMs. So far, we haven't seen any sign of that," he said.

North Korea says its rocket launches are aimed at putting satellites into orbit, claiming it has the right to peaceful use of space. But Pyongyang is banned from such launches under U.N. Security Council resolutions as it has been accused of using them as a cover for testing intercontinental ballistic missiles.

Following Sunday's launch, the Security Council held an emergency meeting and strongly condemned the launch, saying any launch using ballistic missile technology, regardless of whether it's called a satellite launch or anything else, contributes to the North's nuclear weapons delivery system. (Yonhap)