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May 20, 2015, 8:37 AM UTC / Updated May 20, 2015, 8:55 AM UTC / Source : Reuters

SEOUL, South Korea - Photos showing a North Korean missile launched from a submarine were manipulated by state propagandists, a top U.S. military official said on Tuesday.

North Korea, heavily sanctioned by the United States and United Nations for its missile and nuclear tests, said on May 9 it had successfully conducted an underwater test-fire of a submarine-launched ballistic missile. If true, it would indicate progress in its pursuit of building missile-equipped submarines.

On Wednesday, the North warned Washington not to challenge its sovereign right to boost military deterrence and boasted of its ability to miniaturize nuclear warheads, a claim it has made before and which has been widely questioned by experts and never verified.

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An image obtained by Yonhap News Agency showing North Korean leader Kim Jong Un pointing at a ballistic missile his military claimed to have launched from underwater on May 9. KCNA / EPA

But Pyongyang is still "many years" from developing submarine-launched ballistic missiles, U.S. Admiral James Winnefeld told an audience at the Centre for Strategic & International Studies in Washington on Tuesday.

"They have not gotten as far as their clever video editors and spinmeisters would have us believe," said Winnefeld, who is vice chairman of the Joint Chiefs of Staff.

Analysis seen by Reuters from German aerospace engineers Markus Schiller and Robert Schmucker of Schmucker Technologie appeared to support Winnefeld's statement.

The Munich-based pair said photos of the launch were "strongly modified," including reflections of the missile exhaust flame in the water which did not line up with the missile itself.

An image released by North Korea's Rodong Shinmun shows what Pyongyang claimed to be a ballistic missile being launched from a submarine in waters near the northeast coast of Sinpo on May 9. RODONG SINMUN / EPA

North Korea, which regularly threatens to destroy the United States, had a track record of offering faked proof to claim significant advances in missile technology, Schiller and Schmucker said, such as poorly built mockups of missiles on display at military parades in 2012 and 2013.

A photo on state TV showed a missile high in the sky leaving a trail of white smoke, whereas other photos from state media showed no white smoke, suggesting the two photos were of different missiles with different propulsion systems, Schiller and Schmucker said.

- Reuters