MANILA, Nov 21 (AFP) - U.S. Vice President Kamala Harris will reaffirm American commitments to the defence of the Philippines when she meets with President Ferdinand Marcos Jr. in Manila on Monday, a senior U.S. administration official said.

Harris, whose three-day trip to the Philippines includes a stop on the islands of Palawan on the edge of the South China Sea, will also reaffirm Washington's support for a 2016 international tribunal ruling that invalidated China's expansive claim in the disputed waterway.

"The vice president will underscore our commitment to stand up for the international rules and norms because we recognise the impact that that has on Philippine lives and livelihoods," the U.S. official said.

Beijing claims some territories in the waters off Palawan and much of the South China Sea, citing China's own historical maps. The 2016 ruling by an arbitration tribunal in The Hague, however, said the Chinese claims had no legal basis, delivering a victory for Manila.

But the Philippines has been unable to enforce the ruling and has since filed hundreds of protests over what it calls encroachment and harassment by China's coast guard and its vast fishing fleet.

Harris' visit would be the highest-level trip to the Philippines by a Biden administration official and marks a sharp turnaround in relations, which were strained by former President Rodrigo Duterte's animosity toward Washington and his embrace of Beijing.

"The vice president will tell President Marcos that we are pleased to see our security ties in such strong position," the U.S. official said.

Washington and the Philippines have moved ahead with an Enhanced Defense Cooperation Agreement (EDCA) that dates back to the Obama administration and that languished under Duterte.

EDCA allows the United States to maintain a military presence, but not a permanent one, in its former colony through the rotation of ships and aircraft for humanitarian and maritime security operations in mutually agreed Philippine bases.

The United States has proposed adding more EDCA sites to the current five "to deepen our work together," the U.S. official said, adding that Washington has allocated $82 million to complete 21 projects on the five existing locations.

Last week, Philippine military chief Bartolome Bacarro said the United States had proposed including five more bases in the EDCA, including one in Palawan.

Harris is scheduled on Tuesday to meet with coast guard officials and tour a coast guard vessel in Palawan and speak about "principles of sovereignty territorial integrity and freedom of navigation," the U.S. official said.

Apart from security cooperation, the visit aims to strengthen Washington's partnership with the Philippines across a range of issues, including on climate action, nuclear cooperation, and food security, the digital economy, and health and maritime cooperation, the official said.