The US military said Tuesday it planned to help the Philippines monitor its coastal waters as Manila faces an escalating dispute with China over territorial claims.
The Pentagon revised earlier comments and said there was no firm plan to deliver a land-based radar to the Philippines, but that a radar could be part of future assistance.
"We are in the initial planning stages of assisting the Philippines with a National Coast Watch Center," Major Catherine Wilkinson told AFP.
The center is designed "to create an overall picture of what is going on in the Philippines' territorial waters," she said.
"Right now we are discussing a range of options and no details have been finalized. Radars may be an eventual part of the package but it hasn't been determined yet."
The cost and the time line for the project were still being worked out, she said.
The Philippines has requested radar, patrol aircraft and naval vessels as it seeks to bolster its position in a row with China over the Scarborough Shoal, which lies near the main Philippine island of Luzon.
China claims the area along with virtually all of the South China Sea up to the shores of other Southeast Asian nations, including Malaysia, Vietnam and the Philippines.
The Pentagon's comments came after President Benigno Aquino paid a visit last week to the White House, where he was offered a robust show of support.
Plans to help Manila reflect Washington's strategic shift towards Asia amid a growing rivalry with Beijing, with the South China Sea at the center of the contest, analysts said.
"Land-based radar is one of the practical ways the United States can simultaneously boost Philippine defense capabilities and signal Washington's long-term commitment to Asia," said Patrick Cronin, senior adviser for Asia at the Center for a New American Security, a Washington think tank.
China may choose to defuse tensions with the Philippines just before a gathering of the 10-member Association of Southeast Asian Nations next month, Cronin said.
"But it is also possible that China is determined to humiliate the Philippines and, indirectly, the United States," he told AFP.
Manila's request for US military help marks a reversal after the Philippines evicted the American military from its vast naval base at Subic Bay in 1992.
It was unlikely the United States would look at providing military aircraft at a time when China may be preparing a conciliatory gesture, Cronin said.
"If China persists with embarrassing the Philippines, then I have no doubt aircraft sales will follow," he said.
Tensions between Beijing and Manila escalated in April when Chinese and Philippine vessels approached the Scarborough Shoal, which lies near the main Philippine island of Luzon. Manila says the rock formation falls within its exclusive economic zone.