WASHINGTON, May 1 (AFP) - Responding to Beijing's aggressive expansion into the trade routes and strategic islands of the South China Sea headlined talks on Monday (May 1) between President Joe Biden and his Philippines counterpart Ferdinand Marcos Jr at the White House.

Marcos Jr is on a four-day trip that follows last week's state visit to Washington by South Korean President Yoon Suk Yeol and a White House meeting in January between Biden and Japanese Prime Minister Fumio Kishida.

Greeting Marcos Jr in the Oval Office, Biden underlined the "ironclad" US commitment to defending the country.

Marcos Jr referred to "difficult times" and said the Philippines finds itself in a region with "arguably the most complicated geopolitical situation in the world right now".

"So it is only natural for the Philippines to look to its sole treaty partner in the world to strengthen, to redefine, the relationship that we have and the roles that we play in the face of those rising tensions that we see now around the South China Sea and Asia Pacific," he said.

A senior US official said the Marcos Jr visit - which began with a military honour guard outside the White House - was the first "at this level and intensity" between the two countries for decades.

"It is clear that we're in a deeply consequential period in terms of our Indo-Pacific engagements," the official told reporters, speaking on condition of anonymity.