North Korea has recently conducted engine tests for an intercontinental ballistic missile with enough strength to potentially deliver a nuclear warhead to the United States, a U.S. think tank said Friday.
North Korea conducted at least one engine test for the KN-08 missile in late March or early April, the think tank 38 North said, marking the latest in a series of tests for a missile believed to have a range of more than 6,000 miles.
"As this effort progresses, the next technically logical step in the missile's development would be a flight test of the entire system," said 38 North, which is affiliated with Johns Hopkins University's U.S.-Korea Institute, in its report.
Commercial satellite imagery indicates movement and removal of missile parts and fuel tanks as well as changes in the flame trench that point to North Korea having conducted one or more tests of the engine in the two-week period from March 22, the report said.
South Korea's Defense Ministry declined to confirm the specifics of the report citing intelligence policy but said a long-range missile launch by the North could not be ruled out.
It's not clear how long it would take for North Korea to develop a nuclear warhead that could be attached to a missile. Intelligence analysts believe Pyongyang is working on developing a nuclear weapon and the technology to miniaturize a warhead to mount it on a long-range missile.
North Korea successfully put a satellite into orbit in December 2012 on a rocket — the Unha-3. Pyongyang said it was designed for purely scientific missions, but the international community said the launch was a disguised ballistic missile test and the U.N. Security Council tightened existing sanctions as a result.
The Unha-3 stood about 100 feet high, and 38 North said satellite images showed the launch site for the Unha was now being modified to take larger rockets of up to about 165 feet in height.
"Construction may not be completed until early summer, effectively preventing a launch from the facility in the meantime," it said.
The report on the engine testing comes a week after the think tank reported heightened activities at the North's nuclear test site at Punggye-ri, indicating it was ready to conduct a fourth nuclear test.
A South Korean government official said preparations for a nuclear test at Punggye-ri appeared to be complete, including the sealing of tunnels dug into a mountain range, and all that remained was for the North's leader, Kim Jong-un, to order it.
Since 2006, the United Nations has imposed sanctions on North Korea for its nuclear and missile tests, but the North has pushed ahead with further tests, even disregarding warnings from its sole major ally, China.
On Friday, the North's official media carried a report that showed Kim had replaced his top military aide, naming confidant Hwang Pyong-so as the new army political chief.
Hwang replaced Choe Ryong-hae, who was rumored to be in poor health.
The post of the director of the Korean People's Army's General Political Department is seen as the highest position in the North's 1.2 million–strong army.