A Russian spy ship has been lingering for several days just outside U.S. territorial waters to the west of Kauai, which is home to a key missile testing facility.

The Navy confirmed the ship’s presence on Wednesday after it was first reported by the United States Naval Institute.

“U.S. Pacific Fleet is aware of the Russian vessel operating in international waters in the vicinity of Hawaii, and will continue to track it through the duration of its time here,” Capt. John Gay said. “Through maritime patrol aircraft, surface ships and joint capabilities, we can closely monitor all vessels in the Indo-Pacific area of operations.”

The Pacific Fleet didn’t provide more details. USNI quoted defense officials as saying that the ship had been operating within the bounds of international law, was not a hazard to navigation and has not been broadcasting an automatic identification system.

It identified the ship as the Vladivostok-based Kareliya, which specializes in signals intelligence, and said open-source intelligence analysts tracked the vessel which was seen operating about 15 miles to the west of Kauai on Friday.

Kauai is the site of the Pacific Missile Range Facility Barking Sands, which is used by the Navy and the Missile Defense Agency to test-fire missiles.