U.S. Watching Suspicious N.Korean Sub

The U.S. military has ramped up surveillance of a North Korean submarine that has been conducting "unusual activities" in the East Sea for about a week, NHK reported Sunday.

Officials in Seoul declined to confirm any military operation against the sub. "The Romeo-class diesel submarine has been engaged in activities for about a week... Activities by submarines of this class in the area usually last about four days," NHK added.

The 1,800-ton diesel subs were introduced in the 1960s and do not have the capacity to fire ballistic missiles. Each 76 m-long sub has a crew of some 50 sailors and is armed with 14 torpedoes and about 20 mines.

CNN last Thursday said the U.S. "is observing the sub via reconnaissance imagery and the officials said the submarine's patrol had taken it farther [than] it has ever gone, sailing some 100 km out to sea in international waters. The submarine's activity was different than the typical training activity usually observed closer to shore."

Citing the CNN report, the website 38 North at Johns Hopkins University said, "While there are several possible explanations, the most likely is preparations for a test in the near future of an updated Pukguksong-1 [KN-11] submarine-launched ballistic missile or a potentially newer system."

"Sinpo-class submarine and a submersible test stand barge have been repositioned" at the Sinpo shipyard, a possible sign of preparations for the recent submarine voyage, or perhaps for an upcoming missile test, it added.

Back in August last year, the North successfully tested a submarine-launched missile that flew 500 km.

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