North Korea has conducted an engine test of an intercontinental ballistic missile and is believed to plan a test flight of the whole system, according to a US think tank.
The KN-08 missile, which is believed to have a range of more than 10,000km – enough to deliver a nuclear warhead to the USA, has been tested throughout March and April, the think tank 38 North has revealed in a report.
Commercial satellite imagery indicates movement and removal of missile stages and fuel tanks as well as changes in the flame trench that point to North Korea having conducted one or more tests in the two-week period from March 22, the report said
"As this effort progresses, the next technically logical step in the missile's development would be a flight test of the entire system," 38 North said in its report.
South Korea's defence 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 easy to conduct a long-range rocket launch right after an engine test but they may have had other things prepared," ministry spokesman Kim Min-seok said.
North Korea is believed to be developing a nuclear weapon and the technology to miniaturise a warhead to mount it on a long-range missile.
In December 2012 it launched a long-range rocket that successfully put an object into space orbit and in February last year conducted a third nuclear test.
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 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.
North Korea missile tests infographic