Lawyer Jay Batongbacal, director of the University of the Philippines Institute for Maritime Affairs and Law of the Sea, said the joint maritime drills were supposed to improve the country's interoperability with allies and other navies in the region.

"President Rodrigo Duterte has a standing order to us, to me, that we should not involve ourselves in naval exercises in the South China Sea except our national waters, the 12 mile distance from our shores," Lorenzana said.