A classified government document seen by Kyodo News on Friday confirmed that U.S. Navy surveillance planes conduct routine maritime patrol to monitor activities in the disputed South China Sea.

"(There were) confirmed flights of U.S. P3C Orion aircraft over the South China Sea especially (in the contested Spratly Islands)," according to the document.

Last year, Philippine President Benigno Aquino III revealed that Manila was seeking the deployment of P3C Orion spy planes over the disputed sea since the Philippines lacks the capability to monitor its territorial and maritime claims far offshore.