CNN
 — 

The Philippines will provide the United States with expanded access to its military bases, the two countries said Thursday, providing US forces with a strategic footing on the southeastern edge of the South China Sea close to self-ruled Taiwan.

The newly announced deal will give the US access to four more locations under an Enhanced Defense Cooperation Agreement (EDCA) dating to 2014, allowing the US to rotate troops to a total of nine bases throughout the Philippines.

The US has stepped up efforts to expand its Indo-Pacific security options in recent months, amid mounting concerns over China’s aggressive territorial posturing throughout the region.

Speaking during a visit to Manila Thursday, US Defense Secretary Llyod Austin said the US and the Philippines remained committed to strengthening their mutual capacities to resist armed attack.

“That’s just part of our efforts to modernize our alliance. And these efforts are especially important as the People’s Republic of China continues to advance its illegitimate claims in the West Philippine Sea,” said Austin, referencing China’s increased presence in waters close to the Philippines.

Austin did not give the location of the bases to which the US military will gain new access.

Thursday’s announcement follows a spate of high-profile US military agreements throughout the region, including plans to share defense technologies with India, and plans to deploy new US Marine units to Japanese islands.

The US Marine Corps also opened a new base on Guam last week, a strategically important US island east of the Philippines. The location, known as Camp Blaz, is the first new Marine base in 70 years and one day is expected to host 5,000 Marines.

Increased access to military bases in the Philippines would place US armed forces fewer than 200 miles south of Taiwan, the democratically ruled island of 24 million that the Chinese Communist Party claims as part of its sovereign territory despite never having controlled it.

Chinese leader Xi Jinping has refused to rule out the use of military force to bring Taiwan under Beijing’s control, but the Biden administration has been steadfast in its support for the island as provided by the Taiwan Relations Act, under which Washington agrees to provide the island with the means to defend itself without committing US troops.

In November, US Vice President Kamala Harris visited the Philippines to discuss expanded US base access with the recently elected President Ferdinand “Bong Bong” Marcos Jr. Some experts said her visit sent an unambiguous message to Beijing that the Philippines is moving closer to the US, reversing the trend under the previous president, Rodrigo Duterte.

Washington and Manila are bound by a mutual defense treaty signed in 1951 that remains in force, making it the oldest bilateral treaty alliance in the region for the United States.

In addition to the expansion of the EDCA, the US is helping the Philippines modernize its military and has included it as a pilot country in a maritime domain awareness initiative. The two countries also recently agreed to hold more than 500 activities together throughout the year.

Earlier this month, the Philippines announced that 16,000 Philippine and US troops would take part in the annual Balikatan exercise, which is set to take place from April 24 to April 27.

That exercise will include “a live fire exercise to test the newly acquired weapons system of the United States and the Philippines,” an announcement from the state-run Philippine News Agency said.

Formal US ties to the Philippines go back to 1898, when as part of the Treaty of Paris that ended the Spanish-American War, Madrid ceded control of its colony in the Philippines to the US.

The Philippines remained a US territory until July 4, 1946, when Washington granted it independence – but a US military presence remained in the archipelago nation.

The country used to be home to two of the US military’s largest overseas installations, Clark Air Base and Subic Bay Naval Station, which supported the US war effort in Vietnam in the 1960s and early ’70s.

Both bases were transferred to Philippine control in the 1990s, after a 1947 military basing agreement between Washington and Manila expired.