"From 1991, I don't think we ever had any type of connections with North Korea. We never had an embassy there. I don't know about any type of, any single type of cooperation with North Korea," Kharchenko said in an interview with Kyodo News.

He was reacting to a report, published Aug. 14, by a missile expert at a British think tank, citing evidence that North Korea "has acquired a high-performance liquid-propellant engine from illicit networks in Russia and Ukraine."

The new study by Michael Elleman, a senior fellow for missile defense at the International Institute for Strategic Studies, says there is evidence the engine is "based on the Soviet RD-250 family of engines, and has been modified to operate as the boosting force" for North Korea's Hwasong-12 and Hwasong-14.

It adds that such evidence explains North Korea's "astounding" progress in its long-range missile program.

Kharchenko said a state-owned factory known as Yuzhmash in eastern Ukraine did manufacture the RD-250 during the Soviet Union days from 1965 to 1991 -- when Ukraine declared independence -- but beyond that, such parts had not been produced.

"From 1991...not a single engine, not a single rocket intended for military use had been produced in Ukraine," he said.

The New York Times later reported, based on the expert analysis and classified assessments by U.S. intelligence agencies, that North Korea's success in an ICBM test was "made possible by black-market purchases of powerful rocket engines probably from a Ukrainian factory."

North Korea test-fired two ICBMs in July -- the long-range Hwasong-14 -- which could now reach the United States. The Hwasong-12, an intermediate-range missile, was successfully tested in May.

The ambassador said Ukraine has been active in protecting classified information and that it has in the past detained North Koreans on espionage allegations.

He repeatedly said claims of a link between North Korea's missile engine and Ukraine were "strange."

Kharchenko said Ukraine is aiming for a nuclear-free world and is in a cooperative relationship with the Japanese government to achieve that goal.