A close review of photos from North Korea's recent military parade shows that the Kim regime may be closer to building a functional nuclear missile that can threaten the US mainland than previously thought.

While some experts doubt that all the missile launcher tubes driving around Pyongyang really held missiles or posed a much of a threat, Michael Duitsman, a research associate at the Center for Nonproliferation Studies, warned of a small but troubling detail on one of the missiles.

In the picture below, on the right side of the missile, where the cylindrical section meets the nose, the fuselage appears to have been wrapped.

A submarine missile in a military parade in Pyongyang in April. AP Photo/Wong Maye-E

Here's a closer look:

Duitsman told Business Insider in a phone interview that this may be wound filament-reinforced plastic, a very light alternative to metal that can withstand the incredible pressure of rocket motors. Tal Inbar, the head of the space research center at the Fisher Institute for Air and Space Strategic Studies, first pointed this out.

"Part of the parade is them showing us what they're working on," Duitsman said. "Not stuff that's operational, but stuff they're actively working on. They're showing us their intentions."

Duitsman said wound filament-reinforced plastic has up to 10 times the strength-to-density ratio of aluminum and could greatly reduce the weight of a missile.

Referring to the booster portion of the missile as a stage, Duitsman said, "The lighter the stage is, the less propellant you need and the more you can put on top of it." In this case, a lighter missile could be used to carry a nuclear warhead.

North Korea launched a similar missile in one of its more successful tests on February 13. KCNA/Handout via Reuters

While it seems like a small detail, Duitsman said that the Soviets and the US made similar breakthroughs when creating their ICBMs. Ultimately, if the North Koreans had advanced composite materials and plastics in this part of their missile design, it would mean they're further along in their program than many experts suspect.

Though the North Koreans would still face problems in launching and steering the missile, Duitsman said they could begin testing an ICBM that could reach Washington in as little as two or three years.