Vice President Kamala Harris will underscore America's commitment to defending treaty ally the Philippines with a visit that starts Sunday and involves flying to an island province facing the disputed South China Sea, where Washington has accused China of bullying smaller claimant nations.

After attending the Asia-Pacific Economic Cooperation summit in Thailand, Harris will fly to Manila Sunday night to meet President Ferdinand Marcos Jr. the next day for talks aimed at reinforcing Washington's oldest treaty alliance in Asia and strengthening economic ties, a senior US administration official said in an online briefing ahead of the visit.