Two U.S. B52 strategic bombers flew near Chinese fake islands in the South China Sea this week, the Pentagon said on Thursday.

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

Chinese ground controllers sent a radio message to the aircraft, asking, “get away from our islands,” but the aircraft continued its flight undeterred in a clear challenge to China’s territorial claim to the islands, Reuters reported.

See also: China released photos of US Navy, claims it intrudes their sea

Pentagon spokesman Navy Commander Bill Urban said that two bombers made one pas within 12 nautical miles of the islands in what the military refers to as a “freedom of navigation” operation. “The B-52s were on a routine mission in the South China Sea,” taking off from and returning to Guam, he added.

U.S. Secretary of Defense Ashton Carter visited a U.S. aircraft carrier transiting its position in the South China Sea last Thursday, November 5, 2015.

See also: U.S. warning to China, “Make no mistake in 24 hours our destroyer will sail near artificial islands”.

The Boeing B-52 Stratofortress is a long-range, subsonic, jet-powered strategic bomber. The B-52 was designed to carry nuclear weapon and was built by Boeing. -MLD, Pentagon