New satellite images show that North Korea may be modifying its submersible missile test barge at a shipyard on its east coast, a US expert website monitoring the communist country said Sunday.

38 North said commercial satellite imagery taken Saturday (US local time) indicates that a missile canister for the submersible missile test barge has likely been removed.

The removal is "possibly for maintenance, or for the replacement with a new canister or launch frame to accommodate larger submarine-launched ballistic missiles (SLBMs)," the think tank said.

"A truck-mounted crane was observed on the quay next to the drydock, and a probable missile canister was suspended from its raised boom," it said, adding that a cab-over truck was also observed close to the entrance of the construction hall.

The analysis followed a series of recent reports from the same website and a US think tank about activities spotted at the Sinpo shipyard.

38 North has said, citing satellite images, the floating drydock and the submersible missile test barge have recently been repositioned along the submarine launch quay for an "unclear" purpose.

It said the moves could indicate that the North's new ballistic missile submarine "may be nearing completion or is ready to be rolled out and launched in the near future."

North Korea has been building a new submarine, which is believed to be a 3,000-ton one that is capable of carrying three SLBMs. Pyongyang first unveiled the new asset in July 2019. (Yonhap)