The U.S. Navy sailed two Pearl Harbor destroyers near Chinese manmade islands in the South China Sea Monday (Sunday Hawaii time), continuing its “freedom of navigation” campaign aimed at challenging China’s increasing militarization in the contested region.

The USS Chung-Hoon and USS Preble, each with more than 300 crew, “sailed within 12 nautical miles of the Gaven and Johnson reefs in order to challenge excessive maritime claims and preserve access to the waterways as governed by international law,” said Cmdr. Clay Doss, a spokesman for the Navy’s 7th Fleet.

The Spratly Islands passage marks the third time this year that the United States has conducted a freedom of navigation challenge to China’s island-building.

“U.S. forces operate in the Indo-Pacific region on a daily basis, including in the South China Sea,” Doss said in an email. “All operations are designed in accordance with international law and demonstrate that the United States will fly, sail and operate wherever international law allows. That is true in the South China Sea as in other places around the globe.”

It’s been a regular mantra of the United States, even as China has built up considerable military capability including runways, aircraft, missiles and radars on reclaimed former reefs and rocks.

Randall Schriver, assistant secretary of defense for Indo-Pacific security affairs, on Friday promised more of the same.

“I don’t know what steps China will take beyond what they’ve already done,” Schriver said during a briefing on a new report on military and security developments in China.

“I think those steps at militarizing the outposts are designed with a certain aim” in which China seeks to further establish an “illegal, expansive sovereignty claim” over the South China Sea, Schriver said.

China’s actions are destabilizing for the region, and “in response, they’re getting more action from the United States — freedom of navigation, presence operations, joined by more and more countries,” he said.

A French warship sailed through the Taiwan Strait on April 7, angering China, and two U.S. destroyers, the Pearl Harbor-based USS William P. Lawrence and USS Stethem, operating out of Japan, made the passage in late April.

China was disinvited from the Rim of the Pacific maritime exercise in Hawaii in last year “because of their activities in the South China Sea, and there could be more cost imposition in the future,” Schriver said.

Schriver said he didn’t know of any plans to invite China to the next RIMPAC exercise, scheduled for 2020, but as part of the U.S. toolkit, “we cannot only do the (freedom of navigation operations), the presence operations, the capacity building, but (also) cost imposition.”

China Foreign Ministry Spokesperson Geng Shuang said Preble and Chung-Hoon “trespassed” without permission from the Chinese government.

The Chinese Navy identified and verified the U.S. warships “and warned them off,” Geng said. “The trespass of U.S. warships is a violation of China’s sovereignty. It undermines peace, security and good order in the relevant waters.”

Adm. Phil Davidson, head of U.S. Indo-Pacific Command, has acknowledged China’s growing firepower in the South China Sea in late 2018, referencing the new “great wall of SAMs” (surface-to-air missiles). But he has also emphasized U.S. staying power with 60% of Navy ships, 55% of Army forces and two-thirds of Marines in the Indo-Pacific.

Davidson in March said a “general convergence” has emerged “around the idea of a free and open Indo-Pacific” — meaning opposed to China’s strong-arm tactics — with Japan, Australia, New Zealand and other nations putting forth similar concepts.