On Monday, the Philippines and the United States began the largest-ever combined military training in the island nation, signifying increasing security relations as new tensions in the disputed South China Sea arise.

The war drills are the final under outgoing President Rodrigo Duterte, who earlier threatened to halt exercises and sever ties with longtime ally the United States as he shifted his focus to China.

Nearly 9,000 Filipino and American soldiers will participate in the 12-day training exercise across the main island of Luzon, which is normally an annual event but was canceled or reduced due to the pandemic.

At the opening ceremony in Manila, Philippine military head General Andres Centino stated that the greatest iteration of the Balikatan war games demonstrated the two countries' "deepening alliance".

According to US Major General Jay Bargeron, their respective armed services' "friendship and confidence" will allow them to "succeed together across the entire spectrum of military operations."

Maritime security, amphibious operations, live-fire training, counterterrorism, humanitarian assistance, and disaster relief will all be covered in the exercises.

Recent maneuverings between the two countries have centered on the possibility of conflict in the South China Sea.

Since entering office in 2016, Duterte has drawn closer to China but has faced opposition from the Philippine people and military concerns over its territorial ambitions in the seas.

Trillions of dollars in trade pass through the strategic sea, which is also thought to be rich in petroleum deposits, making it a recurrent source of regional conflict.

China has defied a 2016 decision by The Hague-based Permanent Court of Arbitration that its historical claim is unfounded.

It has bolstered its position by erecting artificial islands over several contested reefs and erecting armaments on them.

Tensions spike 

The future of the war games has been called into question after Duterte announced in February 2020 that he intended to terminate the Visiting Forces Agreement, which provides the legal basis for the United States to conduct joint military exercises and operations in the Philippines.

However, he reversed his decision in July, as tensions between Manila and Beijing, ignited by the US, over the South China Sea rose.

The drills are taking place in the shadow of Russia's special operation in Ukraine. The US and its allies are arming Kiev while imposing severe economic sanctions on Moscow.

Duterte, whose six-year tenure expires in June, has expressed concern that the Philippines is "engaged" in the fight due to its security relationship with the US.

This includes a mutual defense treaty and the US military's permission to station defense equipment and supplies on many Philippine facilities.