Story highlights The ship is operating approximately 100 miles off the Alaska coast in international waters, US officials said

It's possible the ship was there to observe the recent successful THAAD missile test off Alaska, they added

(CNN) A Chinese spy ship has been sailing in international waters off the coast of Alaska for several days, having first arrived in the area shortly before the test of a US missile defense system, multiple US officials have told CNN.

US Navy Capt. Scott Miller, spokesperson for the North American Aerospace Defense Command, said the ship is believed to be a "communications" or "intelligence" vessel and confirmed it has been in the area for the last few days.

Miller would not speculate on the reason for the ship being there.

Two US military officials told CNN that the ship is operating approximately 100 miles off the Alaska coast in international waters.

The officials pointed out that the Chinese ship is operating legally and said the US does not have security concerns about the vessel.

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