MANILA (DPA) - US Defence Secretary Mark Esper on Tuesday (Nov 19) vowed more support for the Philippines in its efforts to modernise its military and improve maritime security as tensions build over the disputed South China Sea.

Mr Esper, who was in Manila for a one-day visit, said he and Philippine Defence Secretary Delfin Lorenzana discussed various ways to strengthen cooperation and further boost the two countries' decades-old alliance.

"The United States will continue to support and to help modernise the Philippines armed forces and to improve maritime security and domain awareness," he told a press conference after their meeting.

"We look forward to train in future joint air and maritime patrols to improve our inter-operability and to demonstrate our commitment to upholding the long-standing international rules and norms," he added.

Mr Esper said the United States would continue to conduct freedom-of-navigation operations in the South China Sea, despite warnings by China against such activities, stressing that such acts send a clear message that all countries should abide by international laws.

"I think it is incumbent upon all of us to take a very public posture and to assert our sovereign rights and to emphasise the importance of law," he said.

Noting that the US has conducted more freedom-of-navigation operations in the past year than in the previous 20 years, Mr Esper said: "The clear signal that we're trying to send is not that we oppose China per se, but that we all stand for international rules and international laws and that we think China should abide by them as well."

"Acting collectively is the best way to send that message and to get China on the right path," he added.