Two U.S. bombers recently flew over manmade islands in the South China Sea, the Pentagon confirmed Thursday.

The overflight is the second U.S. operation in the past month in the region where the Chinese claim ownership of several islands that the international community does not recognize as sovereign land.

Pentagon press secretary Peter Cook told reporters on Thursday that the U.S. conducts B-52 flights in international air space over the South China Sea “all the time.”