The Pentagon disinvited China from participating in a major naval exercise on Wednesday, signaling mounting U.S. anger over Beijing’s expanded military footprint in disputed areas of the South China Sea.

Lt. Col. Christopher Logan, a Pentagon spokesman, said the Defense Department had withdrawn an earlier invitation to the Chinese navy to participate in the Rim of the Pacific (RIMPAC) drill, a biennial naval exercise that involves more than two dozen nations, over Beijing’s decision to place anti-ship missiles, surface-to-air missiles and electronic jammers on the Spratly Islands.

Those islands, which China has enlarged and occupied in recent years, are subject to competing claims from several countries, including Malaysia, Vietnam and the Philippines.

“We believe these recent deployments and the continued militarization of these features is a violation of the promise that President Xi [Jinping] made to the United States and the world,” Logan said in a statement.

The Pentagon said that China has also landed bomber aircraft, apparently including the advanced, nuclear-capable H-6K, at Woody Island, in another disputed area to the north claimed by China and Vietnam.

Chinese Foreign Minister Wang Yi, who met with Secretary of State Mike Pompeo in Washington on Wednesday, called the decision “unconstructive.”

“We hope the U.S. will change such a negative mind-set. Both China, the U.S. are big countries, and we are well positioned to have greater cooperation at sea,” Wang said at a news conference. “China is only building civilian and some necessary defense facilities on our own islands. That is the right to self-defense and preservation of every sovereign state.”

The decision to exclude China from the exercise is likely to intensify tensions with a country the Pentagon has identified, along with Russia, as a chief rival to American military power and a focus of planning.

While the U.S. and Chinese militaries coordinate in some areas, the United States has expressed concern about China’s growing arsenal of sophisticated weapons and its attempt to project its might across Asia and beyond.

While the Trump administration does not back any of the rival claims to the islands and smaller features, it has insisted on freedom of navigation and challenged Chinese assertions of sovereignty over virtually all the South China Sea, which U.S. allies in the region see as key to their economic interests and security.

Patrick Cronin, an Asia scholar at the Center for a New American Security, said the move was a “welcome slap” on the wrist in response to China’s buildup in contested waters and its decision to largely ignore a 2016 ruling challenging its maritime claims.

“China’s militarization of the South China Sea deserves to be penalized, not rewarded,” he said.

The Pentagon’s decision may presage a harder line than the Trump administration has previously taken on the South China Sea dispute.

“We have called on China to remove the military systems immediately and to reverse course on the militarization of disputed South China Sea features,” Logan said.

China’s exclusion comes a month before Defense Secretary Jim Mattis is due to make his first official visit to China. It is not clear how the RIMPAC decision, which was authorized by Mattis, may affect that trip.

Cronin said the decision was unlikely to alter China’s plans for the South China Sea. “China’s response will be to adjust its information warfare, but China’s strategy will remain on course, unperturbed by U.S. actions thus far,” he said.

The move occurs at a delicate moment for U.S. strategy in Asia, just weeks ahead of a planned summit between President Trump and North Korean leader Kim Jong Un over that country’s nuclear program. Ahead of the talks, the United States needs Beijing, North Korea’s chief economic backer, to maintain pressure on Pyongyang.

A Pentagon official said that China was notified about its exclusion from the exercises, which last about a month, on Wednesday morning. Beijing began participating in the exercise in 2014.