Recent satellite imagery indicates that North Korea may be building a new submarine larger than its current ballistic missile submarine, a U.S. website monitoring the North said Friday.

"Commercial satellite imagery strongly suggests that a naval construction program is underway at North Korea's Sinpo South Shipyard, possibly to build a new submarine," 38 North said in a report based on analysis of imagery of the North's Sinpo Shipyard.

The imagery shows an approximately 10-meter-in-diameter circular component outside the facility's recently renovated fabrication hall, which may be intended as a construction-jig or as a component for the pressure hull of a new submarine, 38 North said.

"If this activity is indeed to build a new submarine, it would appear to be larger than North Korea's GORAE-class experimental ballistic missile submarine (SSBA), which has a beam of approximately 7 meters," the report said.

Other signatures of submarine construction include appearance and movement of raw steel, fabricated sub-components and finished components around the facilities construction and fabrication halls and parts storage yards, the report said.

North Korea successfully conducted the latest submarine-launched ballistic missile (SLBM) test in late August, sending the missile, designated KN-11, some 500 kilometers over the East Sea, the greatest distance the communist nation has achieved since it began SLBM tests last year.

Moreover, the missile was launched at a high angle, meaning the missile could have flown farther.

The North's SLBM capability, if fully developed, would pose a serious threat because its mobile nature would make it very difficult to detect preparations for a launch. (Yonhap)