US and Philippine Marines stormed a beach near a disputed outcrop in the South China Sea on Friday as part of joint military exercises involving more than 3,500 soldiers.

It is the first time the annual naval drills will be held under Philippine President Ferdinand Marcos, who has expressed strong support for the decades-old alliance after rocky relations under his predecessor Rodrigo Duterte.

Duterte had threatened to cancel drills and scrap a key military deal with the United States as he veered toward China.

But Marcos told US President Joe Biden during a meeting in New York last month that he appreciated America’s role in “keeping the peace in our region.”

China’s recent war games over Taiwan, which it claims as part of its territory, had alarm bells ringing among nations around the South China Sea.

Beijing claims sovereignty over most of the sea, while the Philippines, Vietnam, Malaysia and Brunei have overlapping claims to parts of it.

China has ignored an international court ruling that its claims have no legal basis and has aggressively enforced its stance.

It has built artificial islands and deployed hundreds of Coast Guard and Maritime Militia vessels to roam strategic waters, swarming reefs and harassing fishermen and other boats.

The KAMANDAG drills — the Filipino acronym for “collaboration of warriors of the sea” — began Monday and will run until Oct. 14 on the country’s main island of Luzon.

One of the goals is to improve the coastal defense capability of the Philippine military.

Some 300 soldiers were involved in Friday’s amphibious drills, which were held on an uninhabited beach in Zambales province, about 240 kilometers (150 miles) east of the Scarborough Shoal, which China seized from the Philippines in 2012.

The rich fishing ground has become a focal point between the two countries.

“We are preparing for any threat that will come sooner or later,” said Major Emery Torre, spokesman for the Philippine Marine Corps.

But Torre said the drills didn’t simulate an attack by any particular country and didn’t relate to any specific situation.

Marcos has taken a harder line in defending Philippine waters, insisting he would not allow China to trample on Manila’s maritime rights.

During aerial surveillance over the Scarborough Shoal on Thursday, the Philippine Coast Guard spotted six Chinese vessels, including four Coast Guard boats and two militia boats, in and around the small ring of reefs.

“We are conducting the patrol operations to be present in the area and also in the interest of our fishermen,” Coast Guard spokesman Armand Balilo said.

As regional tensions mount, Washington is keen to maintain its security alliance with Manila, which includes a mutual defense treaty and permission for the US military to stockpile defense equipment and supplies at several Philippine bases.

It also allows US troops access to certain military bases in the country.