President Barack Obama cemented on Monday a 10-year defence pact between the Philippines and the United States that he said is not meant to counter or contain China.
"Our goal is not to counter China, not to contain China," Mr Obama said at a joint news conference with Philippine President Benigno Aquino.
He said the goal "is to make sure international norms and rules are respected".
Mr Obama reiterated that the US will not rebuild old bases or construct new ones in the Philippines.
Mr Aquino, in his remarks, said China "shouldn't be concerned with this agreement".
In a news briefing earlier, the National Security Agency's senior director for Asian affairs Evan Medeiros said: "We're not doing this because of China."
"We're doing this because we have a longstanding alliance partner. They're interested in stepping up our military-to-military engagement," he said.
In a commentary, however, China's state news agency Xinhua called the Philippines a "troublemaker".
"Given that the Philippines is at a bitter territorial row with China, the move is particularly disturbing as it may embolden Manila in dealing with Beijing," it said.
It added that a "more assertive and even reckless Manila" might even "upset" Mr Obama's drive to rebalance US military powers into Asia.
"By striking the defence deal with the United States at this moment despite domestic opposition, the Aquino administration has made its intention clear: to confront China with US backing," it warned.
The "enhanced defence cooperation agreement", signed by Manila and Washington representatives just hours before Mr Obama landed in Manila, will give US access to more Philippine bases, over which Manila will retain full control.
It will also allow the US to "rotate" more troops, warships and planes for longer periods of time. The US currently has a 700-strong counter-terrorism unit active in southern Philippines, but it acts only in an advisory role.
The defence pact is also crafted to help the Philippines more easily acquire newer combat aircraft and warships, and set up the infrastructure it needs to deploy these resources along its borders.
Another provision in the agreement is that the US will be able to build new facilities on existing bases to store humanitarian and disaster relief equipment.