HONG KONG (CNN) - North Korea's test of a rocket engine Sunday showed "meaningful" signs of progress, according to South Korean officials.
"Through this test, it is assessed that (North Korea) has made meaningful progress in engine performance, but further analysis is needed for exact thrust and its possible uses in future," said South Korean Defense Ministry deputy spokesman Lee Jin-woo.
He said the equipment tested "appears to have one main engine with four auxiliary engines connected to it. We believe this was an attempt to develop a new engine."
Two US defense officials told CNN the engine could possibly be used in an eventual intercontinental ballistic missile, but it was unclear if that was its eventual purpose.
Pyongyang, for its part, touted the test as a "great leap forward" in its rocket program.
Many analysts linked the timing of the test to US Secretary of State Rex Tillerson's first visit to north Asia, which ended in Beijing Sunday.
According to the official North Korean news agency KCNA, the test measured the thrust power in the combustion chamber, the structural safety and reliability of the engine, and the movement of the turbine pipe.
The KCNA statement mentioned only civil, rather than military, purposes for the new engines, saying it would "help consolidate the scientific and technological foundation to match the world-level satellite delivery capability in the field of outer space development."
The engine was tested at the Sohae Satellite Launching Station, a major space facility on the country's northwest coast, from which North Korea successfully launched its first satellite into orbit in December 2012.
North Korea insists its space program is peaceful and focused on putting scientific satellites into orbit. However, analysts have long accused Pyongyang of using the program as a covert weapons testing scheme.
As aerospace engineer John Schilling wrote in January, North Korea's primary space launch vehicle, the Unha-3, "could be pressed into service as a crude ICBM."
"An ICBM variant of the Unha could be sufficiently similar to the space launch vehicle in that it would be very likely to succeed, making it a good candidate for a political demonstration even though the Unha would make for a poor missile."
China followed a similar path with its space and ballistic missile program beginning in the 1960s. Engines used in the Long March 2 satellite launcher were later repurposed for the "development of the DF-5 ballistic missile -- China's first true intercontinental range missile," according to David Wright, co-director of the Union of Concerned Scientists.
However, in a recent paper published in the journal Korea Observer, weapons experts Markus Schiller and Theodore Postol wrote that the potential for North Korea to repurpose a space rocket to deliver an ICBM "does not mean that North Korea has the ability, or is likely to have the ability, to use this postulated ICBM to materially threaten the United States with a nuclear attack."
"It is unlikely that North Korea now has a nuclear weapon that weighs as little as 1,000 kg (2,200 lb). It is also unlikely that such a first-generation nuclear weapon would be capable of surviving the unavoidable 50 G deceleration during warhead reentry from a range of nearly 10,000 kilometers (6,200 miles)," they wrote.
"This engine produces enough thrust for the first stage, possibly even the second stage, of a large ICBM," Michael Elleman of the US-based International Institute for Strategic Studies told CNN.
Elleman said that the engine appeared "too large" for the ICBM prototypes that North Korea has demonstrated during military parades, but added "we think they could shrink it down and fit it onto either of the prototypes that they have paraded to date."
While in the past North Korea has been largely dependent on existing -- mostly Soviet and Chinese technology -- Schilling pointed out last year that "we have now seen that North Korea can build large rockets using both solid and high-energy liquid propellants, to their own requirements."
Space and security analyst Markus Schiller suggested on Twitter that the effusive press release put out by KCNA could indicate that "they are finally running their first indigenous engine."
Euan Graham, director of international security at Australia's Lowy Institute, said the North Korea's twin civilian and military rocket programs may have "become so sophisticated they're moving on separate tracks."
He cautioned against underestimating the country's capabilities, pointing to recent submarine launches. "I think a lot of people would have scoffed at the idea that a country of threadbare means like North Korea would be able to test (submarine-launched ballistic missiles)," he said.
Display of force
The rocket engine test came hours before Tillerson met Chinese President Xi Jinping, and a day after America's top diplomat warned that all options -- including military action -- remained on the table when it came to dealing with North Korea.
Sunday's test was a "precisely-timed spectacular," said Peter Hayes, director of the US-based Nautilus Institute, "the kind we've come to expect from Kim Jong Un."
"(The test) was clearly aimed to put pressure on China and to expose the fecklessness of Tillerson's threat to somehow stop the regime," he said.
Graham added that the value of such testing for internal propaganda purposes should also not be ignored.
North Korea operates on a military-first principle, which Kim has increasingly shifted towards nuclear and weapons technology, and away from the traditional standing army.
"Let's not forget the ideological aspect of this," Graham said. "It's important to them to have this ability to demonstrate technological prowess."
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