U.S. Air Force planes joined Philippine jets for a joint patrol amid territorial threats from China.

Three FA-50 jets from the Philippine Air Force and a B-52H bomber from the U.S. Pacific Air Forces carried out a combined air patrol as part of the third Maritime Cooperative Activity (MCA) between the two nations on February 19.

The Philippine Air Force (PAF) said in a statement that the patrol covered areas 90 nautical miles west of Candon City in Ilocos Sur province, and 50 nautical miles northwest of Lubang town in Mindoro.

PAF said: 'This cooperative activity aims to bolster cooperation between the Armed Forces of the Philippines and their US counterparts, thereby enhancing interoperability between its Air Forces.

'With this activity, the PAF underscores its commitment and readiness to support the AFP's efforts in safeguarding the national territory and sovereign rights, and upholding regional peace and security.'

The first leg of the MCA was held in the South China Sea on February 9, in which the Philippine Navy's BRP Gregorio Del Pilar (PS-15) and AW109 Helicopter (NH434) travelled together with the U.S. Navy's USS Gabrielle Giffords in joint drills in the Philippines' Exclusive Economic Zone.

The patrols were conducted amid mounting territorial disputes in the South China Sea.

Communist China currently lays claim over almost the entire South China Sea, one of the world's busiest sea lanes. But a United Nations-backed tribunal in 2016 deemed its claims groundless.