US Secretary of State Antony Blinken and Philippine Foreign Affairs Secretary Teodoro Locsin, in a phone call on Thursday, expressed their shared concerns about Chinese militia vessels in South China Sea, the US State Department said in a statement.
Blinken also reaffirmed that a US-Philippine Mutual Defense Treaty applied to the South China Sea, the statement said.
The Philippines has described the presence of hundreds of Chinese boats inside its 200-mile exclusive economic zone at Whitsun Reef in the South China Sea as "swarming and threatening."
Chinese diplomats have said the boats were sheltering from rough seas and no militia were aboard.
Brunei, Malaysia, the Philippines, Taiwan, China and Vietnam have competing territorial claims in the South China Sea, through which at least $3.4 trillion of annual trade passes.