U.S. experts who have reviewed photos of North Korea's latest intercontinental ballistic missile say the regime has achieved significant technical advancement on its missile program.

CNN on Wednesday quoted Michael Duitsman, a researcher at the James Martin Center for Nonproliferation Studies(CNS), as saying that the missile, dubbed Hwasong-15, is not just big for a North Korean missile but big in general. He said not many countries could build a performing missile of that size that works.

After the launch of the missile Wednesday, the North’s official media outlets have claimed it a success, calling it the completion of its national nuclear forces. South Korean military authorities have also assessed the Hwasong-15 is a new type of missile.

CNS researcher David Schmerler also told CNN that the North’s claim should be taken seriously. He said it is likely the launch was conducted with a dummy warhead equivalent in weight to a nuclear bomb.