The presence of an “intelligence” or “communications” vessel was confirmed by U.S. Navy Captain Scott Miller, a spokesman for the North American Aerospace Defense Command (NORAD).
Military officials aren’t sure what the spy ship  was doing, although it was spotted four days after a test of the Terminal High Altitude Area Defense (THAAD) antimissile system in Alaska.
The ship was 100 miles off the coast but in international waters.
One official told CNN that it was rare for the Chinese to conduct surveillance in the region.
The ship might have been a surveillance ship known as a Tianlangxing , The Diplomat reported. A Tianlangxing passed through the Tsugaru Straight, which links the Sea of Japan and the Pacific, on July 2, The Diplomat reported. Such ships are designed to collect electronic intelligence and track ballistic missiles.
The sighting came just as the U.S., India and Japan were conducting a joint naval exercise in the Indian Ocean. A Chinese spy ship is reportedly monitoring those exercises, too.
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