China-Philippines Tensions in the South China Sea
Overview
In 2023 and 2024, the People's Republic of China (PRC, or China) increased pressure on the Philippines to abandon one of its nine outposts in the Spratly Islands in the South China Sea (SCS) and attempted to deny Philippine vessels access to parts of the Philippines' exclusive economic zone (EEZ) that China claims as its own territory. The escalation of long-standing Sino-Philippine tensions raises the possibility of a crisis or conflict involving China, the Philippines, and potentially the United States. The United States and the Philippines signed a Mutual Defense Treaty in 1951 and a Visiting Forces Agreement in 1998.
Philippine President Ferdinand Marcos Jr., elected in 2022, has refuted China's claims in the SCS more vocally than his predecessor and pursued closer coordination with the United States. Marcos expanded military cooperation with the United States under the 2014 Enhanced Defense Cooperation Agreement (EDCA), which aims to support U.S. strategic interests in the region and modernization of the Armed Forces of the Philippines (AFP).
Some Members of the 117th and 118th Congresses introduced several bills reaffirming the U.S. commitment to the alliance and supporting Philippine efforts to combat PRC aggression. U.S. Secretary of State Marco Rubio reaffirmed the United States' "ironclad support" for the Philippines and criticized the PRC's "dangerous and destabilizing actions" in the SCS in his first call with his Philippine counterpart in January 2025.
Rising Tensions in the South China Sea
Second Thomas Shoal, an atoll in the Spratly Islands, is a potential flashpoint in the SCS (Figure 1). A low-tide elevation and fully submerged at high tide, it is roughly 105 nautical miles (nm) from the Philippine island of Palawan, 620 nm from the PRC, and 22 nm from Mischief Reef, a low-tide elevation in the Spratlys where the PRC maintains an outpost. The Philippines posts a small cadre of marines on a now-derelict Philippine Navy ship, the BRP Sierra Madre, which it grounded on the shoal in 1999 to protect its maritime claims. Since 2013, China has increased its presence near the shoal as part of its stated attempt to end the Philippines' presence there.
In 2023, the China Coast Guard (CCG) and maritime militia vessels—ostensibly private boats that support PRC maritime claims—interfered with Philippine boats resupplying the BRP Sierra Madre. PRC officials have called occupation of disputed features by the Philippines "a red line" for the PRC. Notable incidents included the PRC's targeting of a Philippine Coast Guard boat with a military-grade laser, and using water cannons against, surrounding, and colliding with Philippine vessels. In December 2023, China engaged in what the Philippine government called a "serious escalation" in the SCS. PRC vessels reportedly swarmed the area near Second Thomas Shoal and "harassed, blocked, and executed dangerous maneuvers," resulting in a collision between a PRC coast guard ship and a Philippine boat on a resupply mission. Each side accused the other of ramming one of its vessels. A CCG spokesperson stated its December 2023 actions were "professional, standardized, legitimate, and legal."
The Philippines successfully resupplied the BRP Sierra Madre on several occasions in 2023 and 2024, despite PRC obstruction. The U.S. Department of State issued statements critical of PRC actions and supportive of the Philippines' right to operate in waters around Second Thomas Shoal.
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Source: CRS. Boundaries from U.S. Department of State. |
In June 2024, CCG personnel boarded a Philippine rigid hull inflatable boat, assaulted AFP marines, and destroyed equipment. In a separate incident, a Philippine marine lost his thumb when a PRC vessel rammed his boat as it sought to resupply the BRP Sierra Madre. Following these incidents, in July 2024, the two countries agreed to a provisional agreement regulating future resupply missions. The Philippines has successfully resupplied the derelict ship in the months since, and the two countries agreed to maintain the accord in January 2025 despite ongoing PRC harassment elsewhere in the South China Sea.
In April 2024, the Philippines deployed its largest coast guard vessel, the BRP Teresa Magbanua, to Sabina Shoal, an unoccupied feature in the Spratlys, responding to reports of crushed coral. China responded by sending CCG vessels, which later rammed Philippine Coast Guard boats and prevented the resupply of the BRP Teresa Magbanua. The Philippine vessel withdrew in September, citing bad weather, lack of supplies, and sick crew.
Since 2012, the PRC has harassed and blocked Philippine fishing boats operating near Scarborough Shoal, a traditional fishing area for both countries. In December 2023, the CCG deployed a water cannon on Philippine vessels attempting to deliver provisions to Filipino fishermen near the shoal. In 2024, incidents included dangerous aerial maneuvers by PRC fighter jets around Philippine military and civilian aircraft and the deployment of the PRC's largest coast guard ship to the area.
SCS Disputes and International Law
An arbitral tribunal convened under the United Nations Convention on the Law of the Sea (UNCLOS) ruled in 2016 that the "Nine-Dash Line," which China uses to mark its territorial claims in the SCS, has "no legal basis," and that several PRC actions in the SCS violated the Philippines' sovereign rights. The tribunal found that Second Thomas Shoal, Scarborough Shoal, and the PRC-occupied Mischief Reef fall within the Philippines' EEZ, and that China had unlawfully interfered with Philippine fishing at Scarborough Shoal and created a risk of collision. China declared the ruling "null and void." (For more on the disputes, see CRS In Focus IF10607, China Primer: South China Sea Disputes.) Successive U.S. Administrations have urged both the PRC and the Philippines to abide by the 2016 ruling. The United States is not a party to UNCLOS.
U.S.-Philippines Mutual Defense Treaty
Under Article IV of their Mutual Defense Treaty, the United States and the Philippines each agree that "an armed attack in the Pacific Area on either of the Parties would be dangerous to its own peace and safety and declares that it would act to meet the common dangers in accordance with its constitutional processes." Article V defines such an armed attack as including an attack on the "metropolitan territory of either of the Parties, or on the island territories under its jurisdiction in the Pacific or on its armed forces, public vessels or aircraft in the Pacific." The Treaty does not specifically refer to the SCS. Bilateral Defense Guidelines issued by the alliance in 2023 reinforce treaty obligations, stating that an armed attack "anywhere in the South China Sea," on either country's "public vessels, aircraft, or armed forces—which includes their Coast Guards—would invoke mutual defense commitments."
U.S.-Philippines Security Cooperation
The Philippines has been one of the largest recipients of U.S. military assistance in the Indo-Pacific region, including $40 million in Foreign Military Financing (FMF) in FY2023 and assistance under the Department of Defense's Indo-Pacific Maritime Security Initiative. In 2024, the Biden Administration pledged to work with Congress to provide the Philippines with $500 million in FMF from emergency supplemental appropriations for FY2024 (P.L. 118-50). In February 2025, the Trump Administration reportedly exempted $336 million in assistance for Philippines military modernization from the Administration's freeze on foreign aid.
Under EDCA, the two countries agreed to deepen military cooperation, upgrade certain Philippine military facilities, and allow U.S. forces rotational access to these facilities. In 2023, the number of these bases expanded from five to nine. The United States and the Philippines engage in approximately 20 military exercises and events annually, including combined patrols in the SCS. A 2024 U.S.-Japan-Philippines trilateral meeting included agreements on maritime security and economic cooperation.
In April 2024, U.S. forces deployed a Typhon missile system to the Philippines for use in a military exercise. The missile system's range encompasses the SCS and the Taiwan Strait. The missile system remained in the Philippines following the conclusion of the exercise, and President Marcos has said the Philippines will purchase the system. The PRC criticized that statement.
Considerations for Congress
U.S. options to support Philippine efforts to defend its sovereign rights within its EEZ include U.S. military, quasi-military, and diplomatic actions. Congress may consider whether to support, shape, or curtail such efforts, including through oversight, appropriations and authorizations, legislative directives, and policy statements.
Military options include sending U.S. forces to support Philippine troops on the BRP Sierra Madre, U.S. Navy escorts to Philippine defensive missions, and assistance shoring up the failing vessel. Some observers caution a direct U.S. military role supporting the Philippines could increase the risk of an incident between U.S. and PRC forces. In June 2024, the Philippines reportedly turned down U.S. offers to assist to avoid provoking Beijing. Some recommend less direct U.S. support, such as additional military assistance and training for the AFP; expanding the U.S. presence in the region; coordinating with other claimants to counter PRC actions; and engaging in U.S.-China consultations to prevent unintended escalation.
Non-military options could involve the U.S. Coast Guard (USCG). The U.S. and Philippine coast guards regularly conduct exercises and engagements. In October 2024, the U.S. Department of State's Bureau of International Narcotics and Law Enforcement announced $8 million in new funding to support modernization of the Philippine Coast Guard. The USCG's FY2025 Unfunded Priorities List included support for cutter deployments, regional infrastructure improvements, and regional engagements.
Congress also may consider how U.S. accession to UNCLOS would impact U.S. diplomacy. Since the treaty entered into force in 1994, the United States has accepted and acted in accordance with customary international law as reflected in UNCLOS's provisions on navigation and overflight. (See "Whether United States Should Ratify UNCLOS," in CRS Report R42784, U.S.-China Strategic Competition in South and East China Seas: Background and Issues for Congress.)