WASHINGTON, Aug 15 (INP) North Korea’s success in testing an intercontinental ballistic missile that appears able to reach the United States was made possible by black-market purchases of powerful rocket engines probably from a Ukrainian factory with historical ties to Russia’s missile program, according to an expert analysis published Monday and classified assessments by American intelligence agencies, The New York Times said Tuesday. 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 cyber attacks 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. Such a degree of aid to North Korea from afar would be notable because President Trump has singled out only China as the North’s main source of economic and technological support. He has never blamed Ukraine or Russia, though his secretary of state, Rex W. Tillerson, made an oblique reference to both China and Russia as the nation’s “principal economic enablers” after the North’s most recent ICBM launch last month. 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. 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. 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. On Monday, after this story was published, Oleksandr Turchynov, a top national security official in the government of Mr. Poroshenko, denied any Ukrainian involvement. INP/AH