"And that includes a period in which the United States provided $1.35billion (£1.08billion) in assistance to North Korea as an encouragement to take a different pathway". Of the North Korean rocket and missile projects that we are now aware of, the best fit for this engine would be as the second stage of the new satellite launch vehicle provisionally known as the "Unha-9".
The sole survivor, identified as Kim Kyong Nam, said all the workers could have survived had they left the premises as soon as they heard the sound of the collapse, which they didn't.
Company director from North Korea said to have had business ties with Kim Jong Nam and may have given Pyongyang his travel plans, according to South Korean media. A 2009 resolution of the United Nations bans North Korea from exporting arms or related military equipment.
North Korea's nuclear facility at Yongbyon is well known, but striking it could cause an environmental disaster.
Kim called the test "a great event of historic significance" for the country's indigenous rocket industry, the KCNA report said.
"Some of these technologies which the North Koreans are including in their rocket expansion program actually have to do with a covert method of firing missiles without being detected in advance of actually exploding the devices". There is a major effort underway to keep track of North Korean mobile launchers.
Albright cautioned that a pre-emptive strike carries the risk of "a conventional war involving North and South Korea with large numbers of casualties".
FILE - A North Korean woman stands behind the counter at a souvenir shop in Rajin, North Korea, inside the Rason Special Economic Zone.
The test was conducted at the Sohae launch site and meant to gauge the thrust power, and the safety and control features of the new engine design. "You are talking about hundreds of thousands of casualties, if not millions".
While he was the deputy head of the North Korean Embassy in London, Thae said he visited VOA's Korean Service website "almost every day" and that North Korea's Foreign Ministry also monitors VOA and other media outlets such as Japan's state broadcaster NHK every day.
Seoul, the capital of South Korea, is just 35 miles from the border with North Korea.
"The rail-mounted environmental shelter has been moved up against the engine test stand since Feb 5, either for maintenance or to position a rocket engine for testing", 38 North said in a note.
"All these things always lead people to think that a negotiated, well-verified solution is by far the preferred option", said Albright.