Washington (CNN) North Korea may be close to launching a submarine capable of firing missiles and is making efforts to conceal its preparations, new commercial satellite images obtained by CNN appear to show.

The images from the Middlebury Institute and Planet Labs, appear to show North Korea making progress readying the vessel at the Sinpo South Naval Shipyard along the central coast of the country off the Sea of Japan.

North Korean leader Kim Jong Un visited the base in July to inspect progress on the submarine, which may already be operational, according to analysts.

"North Korea has erected a structure in the secure boat basin to hide the new submarine," said Jeffrey Lewis, director of the East Asia Nonproliferation Program at the Middlebury Institute. "This suggests that the submarine has been launched or will be soon."

CNN has asked the Pentagon for comment.

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