This is reported in an expert analysis published Monday and classified assessments by American intelligence agencies, Censor.NET reports citing The New York Times.
The studies may solve the mystery of how North Korea began succeeding so suddenly after a string of fiery missile failures, some of which may have been caused by American sabotage of its supply chains and cyberattacks on its launches. After those failures, the North changed designs and suppliers in the past two years, according to a new study by Michael Elleman, a missile expert at the International Institute for Strategic Studies.
Analysts who studied photographs of the North's leader, Kim Jong-un, inspecting the new rocket motors concluded that they derive from designs that once powered the Soviet Union's missile fleet. The engines were so powerful that a single missile could hurl 10 thermonuclear warheads between continents.
Those engines were linked to only a few former Soviet sites. Government investigators and experts have focused their inquiries on a missile factory in Dnipro, Ukraine, on the edge of the territory where Russia is fighting a low-level war to break off part of Ukraine. During the Cold War, the factory made the deadliest missiles in the Soviet arsenal, including the giant SS-18. It remained one of Russia's primary producers of missiles even after Ukraine gained independence.
But since Ukraine's pro-Russian president, Viktor Yanukovych, was removed from power in 2014, the state-owned factory, known as Yuzhmash (Pivdenmash), has fallen on hard times. The Russians canceled upgrades of their nuclear fleet. The factory is underused, awash in unpaid bills and low morale. Experts believe it is the most likely source of the engines that in July powered the two ICBM tests, which were the first to suggest that North Korea has the range, if not necessarily the accuracy or warhead technology, to threaten American cities.
"It's likely that these engines came from Ukraine - probably illicitly," Mr. Elleman said in an interview. "The big question is how many they have and whether the Ukrainians are helping them now. I'm very worried."
Bolstering his conclusion, he added, was a finding by United Nations investigators that North Korea tried six years ago to steal missile secrets from the Ukrainian complex. Two North Koreans were caught, and a U.N. report said the information they tried to steal was focused on advanced "missile systems, liquid-propellant engines, spacecraft and missile fuel supply systems."
Investigators now believe that, amid the chaos of post-revolutionary Ukraine, Pyongyang tried again.
Mr. Elleman's detailed analysis is public confirmation of what intelligence officials have been saying privately for some time: The new missiles are based on a technology so complex that it would have been impossible for the North Koreans to have switched gears so quickly themselves. They apparently fired up the new engine for the first time in September - meaning that it took only 10 months to go from that basic milestone to firing an ICBM, a short time unless they were able to buy designs, hardware and expertise on the black market.
The White House had no comment when asked about the intelligence assessments.
Last month, Yuzhmash denied reports that the factory complex was struggling for survival and selling its technologies abroad, in particular to China. Its website says the company does not, has not and will not participate in "the transfer of potentially dangerous technologies outside Ukraine."
American investigators do not believe that denial, though they say there is no evidence that the government of President Petro O. Poroshenko, who recently visited the White House, had any knowledge or control over what was happening inside the complex. How the Russian-designed engines, called the RD-250, got to North Korea is still a mystery.
It is unclear who is responsible for selling the rockets and the design knowledge, and intelligence officials have differing theories about the details. But Mr. Elleman makes a strong circumstantial case that would implicate the deteriorating factory complex and its underemployed engineers.
"I feel for those guys," said Mr. Elleman, who visited the factory repeatedly a decade ago while working on federal projects to curb weapon threats. "They don't want to do bad things."