North Korea is believed to have conducted the recent test of a submarine-launched ballistic missile from a submerged barge, not from a submarine as claimed by the communist nation, a U.S. expert said Tuesday.

Joseph Bermudez, a top North Korea military expert, also said the North appears to have "photoshopped" images of the test to exaggerate progress in its SLBM development, saying the photo released by Pyongyang shows no flame coming from the missile's engine when a "bright pink shadow" was reflected in the water.

The assessment, disclosed during a discussion hosted by the website 38 North, suggests that the North has not made as much headway as previously feared in the development of submarine ballistic missiles, even though the regime is making progress.

The North claimed Saturday that leader Kim Jong-un oversaw a successful underwater test-launch of a "strategic submarine ballistic missile." The test, if confirmed, would represent a significant step forward in the North's missile technology.

"The North Korean press says it was launched from the submarine. I have some significant doubts whether that's true," Bermudez said, citing satellite imagery taken of the North's Shinpo Shipyard a day after the missile test, which shows a submarine docked next to a barge.

The North must have tested the missile from the barge, the expert said, speaking via a video link from Colorado, where his AllSource Analysis is based.

Noting that the North launched the submarine only in October last year, Bermudez emphasized it is almost impossible for the regime to test an SLBM from the vessel only six to seven months later. Such a submarine-based test is at the" very, very outside of any possible North Korean technology at the moment," he said.

"Typically what you do when you develop and test a ballistic missile that is to be launched from a submarine, you test it first on land, then from barges or submersible containers and then eventually you conduct a test from a submarine," he said.

"If you look at the imagery the way North Korea portrays on KCNA, you are given the impression or you're left with the impression that the submarine itself conducted the launch. I have some serious doubts about that at this point in time," he said.

Bermudez also said that the missile used in the test is believed to be much shorter than the North's Musudan or Nodong missiles, citing the size of what appeared to be a ballistic missile shipping container adjacent to the submarine in the satellite imagery.

"So this would suggest that North Korea's developing a new missile. Some people point at the KN-11. We really don't know at this point," he said.

The expert also raised suspicions that the North released manipulated photos.

"If you look at some of the imagery that was provided by KCNA, some things don't match up," Bermudez said, referring to Pyongyang's official news agency.

One of the KCNA photos shows "a bright pink shadow in the water, reflection in the water, from the missile launch," which he said can be expected only if a flame comes from the missile's engine, he said.

"However, in the image, there is no flame visible. There is just smoke and water and steam," he said. "This might suggest that some of the imagery that was provided to the public was photoshopped or manipulated in some fashion to give it a different impression."

Bermudez also said that the North has repeatedly conducted "camouflage, concealment and deception operations."

For now, the North's submarine capabilities are only an "emerging threat," the expert said.

"We're not looking at a dramatic increase in submarine capabilities while we're looking at incremental improvements in submarine capabilities, incremental expansion of submarine force and incremental development of ballistic missiles," he said.

Joel Wit, head of 38 North, also said the North is years away from developing submarine missile capabilities.

"Even with a very strong, maximum effort, in five years, they might be able to deploy ballistic missile submarines with help from overseas, but those submarines would not pose a threat to the United States, and once again, be more of a regional threat," he said.

South Korea's defense ministry described the North's missile launch as "very serious and worrying," and urged Pyongyang to cease the development of such missiles, even though officials said the missile appeared to have flown only about 100 or 150 meters from the surface of the water.

President Park Geun-hye also called it a "serious challenge."

The North's SLBM, if developed, would pose a serious threat because its mobile nature would make it very difficult to detect preparations for a launch. The North's new road-mobile intercontinental ballistic missile, KN-08, has also been a serious concern to the U.S. (Yonhap)