WASHINGTON - Ukraine has released footage of two North Korean spies photographing what they thought were top-secret missile designs in a sting operation, as the country seeks to dispel claims that Pyongyang may have used designs stolen or originating from Ukraine in its development of intercontinental missile technology.

CNN said it was given the footage of the sting operation by Ukrainian security services.

The grainy surveillance video was filmed on July 27, 2011, on a hidden camera set up within a garage to capture the end of a sting operation that was planned ahead. The the video, Ukrainian security service agents can be seen bursting in and arresting the two suspects.

"The images are a little grainy, but in the half-light of a dusty Ukrainian garage, you can sense the unbridled enthusiasm of the two North Korean spies who are photographing what they think are top-secret missile designs,'' CNN reported, adding that the two men were eventually jailed.

Court papers from their 2012 trial showed that the North Koreans were seeking information on "ballistic missiles, missile systems, missile construction, spacecraft engines, solar batteries, fast-emptying fuel tanks, mobile launch containers, powder accumulators and military government standards," said the CNN report.

Some of the information is related to the SS-24 Scalpel intercontinental ballistic missile. The SS-24 Scalpel, also known as the RT-23, is a solid-fueled missile capable of carrying up to 10 warheads launched via missile silos or railroad cars, the report said.

An officer with the Ukrainian security service, who worked on the case, told CNN that it was "impossible" that North Korea had obtained any missile technology from Ukraine as he was sure their espionage attempts had all been intercepted.

In 2011, two other North Koreans were deported after they were caught trying to obtain missile munitions and homing missile devices, particularly for air-to-air class missiles, the officer said.

A third North Korean, tasked with transporting the actual devices out of Ukraine, was also deported, said the report.

In 2015, the officer told CNN that five North Koreans were deported for "assisting North Korea's intelligence work in Ukraine, but he did not elaborate.

Besides the two North Koreans in jail for the 2011 case, there were no other North Korean spies left in Ukraine, the officer said. Those not deported by Ukraine had been voluntarily withdrawn - many working in alternative medicine centres, CNN quoted the officer as saying.

Ukraine has in recent weeks denied that it has ever supplied defence technology to North Korea.

The New York Times recently cited a new study by missile expert Michael Elleman from the International Institute for Strategic Studies (IISS). He said 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 programme.

The factory was identified as Yuzhmash, a state-owned concern. But the factory said it had not produced military-grade ballistic missiles since independence from the former Soviet Union in 1991.

"In the years of independence, Yuzhmash has not produced, and is not producing, missiles and military missile systems," it said in a statement on the company's website.

On July 4, North Korea tested an intercontinental ballistic missile (ICBM) for the first time, saying it can launch a missile that can reach the continental US. The missile, Hwasong-14, was tested again three weeks later, this time in a night launch.

On Aug 8, North Korea's army threatened to fire missiles towards Guam, after US President Donald Trump warned Pyongyang that it will be "met with fire and fury" if it did not stop threatening the US.