MOSCOW -- A recent theory that the intercontinental ballistic missiles North Korea tested in July were built using Soviet engines has raised questions over the potential involvement of Russian President Vladimir Putin in Pyongyang's arms development.

The theory was sparked by an August report by Michael Elleman, senior fellow at the U.K.-based International Institute for Strategic Studies. In it, Elleman claimed that North Korea had acquired an improved version of a Soviet liquid-propellant engine produced by Yuzhmash, a state owned manufacturer based in the Ukrainian city of Dnipro.

This would explain how North Korea, which had occasionally failed to launch even intermediate-range ballistic missiles, improved its abilities so dramatically in recent years. Developing an ICBM is an expensive undertaking that takes decades. The only countries in the world that have fully succeeded so far are the U.S., Russia, China, India and Israel.

Black market routes

Military technology developed during the Soviet era made its way to China and other emerging countries in the aftermath of the Soviet Union's collapse in 1991. Many Russian and Ukrainian experts agree that North Korea is using Soviet technology in its missile program.

The questions is when, and how, Pyongyang got a hold of the engines. Elleman suspects the engines were transported through Russia by train to North Korea sometime in the last two years.

Ukraine's ties with Russia soured quickly after a pro-Western faction took power there in 2014. With orders from Russia drying up, Yuzhmash faced significant financial challenges and was often late in paying employees -- ripe conditions for a leak.

But some believe Pyongyang had access to sensitive information even before then. In 2011, two North Korean nationals working for trade representatives stationed in Belarus were arrested in Ukraine for allegedly trying to steal missile technology. Liquid-propellant engines are extremely complex, and would take more than 10 years to produce even after obtaining the full schematics, said Alexander Degtyaryov, chief designer at Ukraine's Yuzhnoye State Design Office, which has been developing missiles with Yuzhmash since the Soviet era.

Through last year's testing of intermediate-range missiles, North Korea is believed to have made significant progress in heat-proofing missile warheads for re-entry into the atmosphere. It may have decided to ramp up its long-hidden ICBM development now that other technologies necessary for a successful missile strike are coming along, a European military attache in Moscow said.

Russian motives

Missile technology likely made its way to North Korea through the black market. Both Russia and Ukraine have significant problems with corruption, and have been targeted by criminal organizations looking to acquire and sell classified information. They tied for 131st out of 176 countries and regions in Transparency International's Corruption Perceptions Index last year.

The Ukrainian government swiftly issued a statement refuting Elleman's report. Given the backing it receives from the U.S., it has little motivation to support North Korea. While it is possible some corrupt officials may have been involved, it is extremely unlikely that the government was as a whole, according to Vadim Karasev, Director of the Institute of Global Strategies in Ukraine.

Meanwhile, some suspect Russia purposefully allowed North Korea to access ICBM-related know-how. Russia possesses extensive missile technology, including on producing rocket fuel and other necessary components. It has also sided with North Korea against the U.S.

"Smaller countries can see no other way to protect their independence, security and sovereignty but by acquiring nuclear weapons," Putin said back in June in regards to North Korea. Russia also launched a ferry service to and from North Korea in May.

By overwhelming the U.S. with the North Korea issue, Putin is diverting America's attention away from the Middle East and expanding Russian influence in the region, a diplomatic source said.

Regardless of Putin's intentions, protracted tensions between the U.S. and Russia have begun to directly affect North Korea's missile development. It is highly likely that the missile Pyongyang launched over Japan on Aug. 29 used Soviet technology provided by Russia, said Yuri Fedorov, a renowned Russian military expert.