Manila, Philippines - American and Philippine defense chiefs signed an agreement Monday on sharing classified military information and technology, as the long-time treaty allies deepen cooperation in a bid to counter Chinese influence in the region.

US Defense Secretary Lloyd Austin signed the deal with his Philippine counterpart Gilberto Teodoro at the start of a visit to Manila that will also include a meeting with President Ferdinand Marcos.

The General Security of Military Information Agreement allows for the sharing of classified information that could benefit a US ally's national defense, and streamlines the sale of certain classified technologies, officials said.

Austin and Teodoro did not make any remarks at the signing ceremony, but the Philippine defense department said the document was "a critical step to enhance information sharing and deepen interoperability between the Philippines and the US."

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It comes as the Marcos government pushes back against Beijing's territorial claims in the South China Sea and as president-elect Donald Trump prepares to return to office.

China has brushed aside an international ruling that its claims have no legal basis, and has deployed navy and coast guard vessels that Manila says harass its vessels and stop them accessing some reefs and islands in the waters.

This has led to violent confrontations that have resulted in injuries to Filipino personnel and damage to their vessels in the past 18 months.

The US has also conducted joint military drills in the area with the Philippines and other countries, exacerbating tensions in the region.

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All of that has sparked concern the US could be drawn into an armed conflict due to its mutual defense treaty with the Philippines.

The Philippine defense department said Austin is due to visit the western island of Palawan on Tuesday for a meeting with Filipino forces responsible for patrolling the South China Sea and defending outposts.