[1/2] U.S. President Joe Biden listens during the annual White House Correspondents Association Dinner in Washington, U.S., April 29, 2023.
Marcos, who became president last year, has sought warm relations with both the United States and China, who are vying for influence in the Asia-Pacific region.
"Some of the steps that China have taken have concerned (Marcos), probably even surprised him," said one senior Biden administration official.
Experts say the United States considers the Philippines a potential location for rockets, missiles and artillery systems to counter a Chinese amphibious assault.
"We're standing shoulder to shoulder in the South China Sea, where our alignment has never been stronger," said one U.S. official.