The Philippines and the United States have begun a series of military exercises. The army-to-army drills are focused on enhancing the Southeast Asian country's ability to protect and defend its territory from external threats. They come amid China's increasing assertiveness in the South China Sea.

Around 3,000 Filipino and US soldiers are participating in the three-week long annual exercises.

This year's drills will focus on scenarios involving air and sea defense of the Philippine archipelago from foreign aggressors.

Philippine Army Commanding General, Lt. Gen. Romeo Brawner spoke at the opening ceremony, saying "Developments in the region in the recent months have given the Philippine Army cause to shift its focus from internal security to territorial defense."

Most of the activities will take place at Fort Magsaysay, about 160 kilometers north of Manila. It is the Philippines' largest military camp and one of the existing sites that Washington has access to under its Enhanced Defense Cooperation Agreement with the country.

Last month, the Philippines agreed to expand US access to a total of 9 of its military bases as part of measures to ramp up deterrence against China.

Next month, Manila and the US are set to hold their largest-ever annual war games that will involve more than 17,000 troops.