MANILA/WASHINGTON (Reuters) – The Philippines Supreme Court on Tuesday declared constitutional a security deal with the United States allowing an increased U.S. military presence in the former U.S. colony as tension rises in the South China Sea.

Dozens of anti-U.S. activists held protests outside the court denouncing the deal as a de facto basing agreement that would make the Philippines a launching pad for military intervention in the region.

Manila has long been a staunch U.S. ally and the pact is widely seen as important for both sides, worried by China’s increasingly assertive pursuit of territorial claims in the disputed South China Sea.

The court voted 10-4 to deny a petition of some lawmakers and activists to declare the Enhanced Defence Cooperation Agreement (EDCA) unconstitutional because it surrendered Philippine sovereignty to a foreign power.

“EDCA is not constitutionally infirm,” said Supreme Court spokesman Theodore Te. “It remains consistent with existing laws and treaties that it purports to implement.”

In Washington, U.S. Secretary of State John Kerry and Defense Secretary Ash Carter welcomed the court’s decision as they began talks with their Philippine counterparts on security and economic issues, including tensions in the South China Sea and the Trans-Pacific Partnership trade deal.

“The United States has an iron-clad commitment to the security of the Philippines,” Kerry said in opening remarks. “To that end we welcome the Philippines Supreme Court’s decision … (and) look forward to implementing this accord,” he added.

Philippine Defense Minister Voltaire Gazmin said security cooperation with the United States had become more intertwined amid increasing tensions over the South China Sea.

“While we grapple with non-traditional security concerns and natural … disasters, traditional security challenges, to include territorial and maritime disputes, remain … fundamental concerns,” he said. “Given this strategic context, we should be in a position to address such common concerns, as well as contribute to regional peace and stability.”

The pact, signed days before U.S. President Barack Obama visited the Philippines in 2014, will allow U.S. troops to build facilities to store equipment for maritime security and humanitarian and disaster response operations, in addition to giving broad access to Philippine military bases.

U.S. Senate Armed Services Committee Chairman John McCain called it “a landmark agreement … (that) will bring our alliance to a level of cooperation and integration that we have not witnessed in decades.

“As Manila finds itself the target of Chinese coercion in the West Philippine Sea and is looking to Washington for leadership, this agreement will give us new tools to … expand engagement with the Philippine Armed Forces, and enhance our presence in Southeast Asia,” he said in a statement.

McCain said he looked forward to implementation this year of a congressional Maritime Security Initiative he has championed that will provide resources to build the maritime capacity of the Philippines and other Southeast Asia countries.

Philippine military officials say there has been an increase in U.S. exercises, training and ship and aircraft visits in the past year under Obama’s “rebalance” of U.S. forces and diplomatic efforts to Asia in the face of China’s rise, but the pact would take the relationship a step further.

China claims almost all the South China Sea, which is believed to have huge deposits of oil and gas, and has been building up facilities on islands it controls.

Brunei, Malaysia, Vietnam, Taiwan and the Philippines also have claims. Tension rose this month when China began test flights on Fiery Cross Reef, one of three artificial islands where Beijing has constructed airfields.

(Reporting by Manuel Mogato in Manila; Additional reporting by David Brunnstrom, Andrea Shalal and Lesley Wroughton in Washington; Editing by Nick Macfie, Dan Grebler and James Dalgleish)