Washington, Jul 14 (IANS): 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 defence system, the media reported.

US Navy Captain Scott Miller, spokesperson for the North American Aerospace Defence Command, told CNN late Thursday 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.

US ships also regularly operate in international waters near China.

The officials said it is possible the ship was there to observe the latest successful Terminal High Altitude Area Defecse (THAAD) missile system test off Alaska, but the US has not confirmed it.

China has long protested the US-South Korea decision to deploy THAAD to the Korean peninsula, saying that it could be used to target Chinese missiles.

South Korean and US officials say the system would be used to intercept missiles coming from North Korea.