WASHINGTON (REUTERS) - A US B-52 strategic bomber flew near artificial Chinese islands in the South China Sea recently and was contacted by Chinese ground controllers but continued its mission undeterred, the Pentagon spokesman said on Thursday.

"We conduct B-52 flights in international air space in that part of the world all the time," Pentagon spokesman Peter Cook told a news briefing in response to a question about the flight.

"There was one B-52 flight... there was an effort made by Chinese ground controllers to reach out to that aircraft and that aircraft continued its mission unabated. Nothing changed."

Cook said he was not sure when exactly the flight occurred.

Last month, a US warship challenged territorial limits around one of China's man-made islands in the Spratly archipelago with a so-called freedom-of-navigation patrol, the most significant US challenge yet to territorial limits China claims around its new islands.

China claims most of the South China Sea, through which more than US$5 trillion (S$7.1 trillion) in global trade passes every year.

Vietnam, Malaysia, Brunei, the Philippines and Taiwan have rival claims.

The United States has said it will continue conducting the patrols.

US and Chinese warships and aircraft regularly communicate when operating near each other in Asian waters, US military officials say.