Defense Secretary Pete Hegseth issued a harsh warning Saturday about Chinese military aggression in the South China Sea during remarks to a meeting of Southeast Asian defense ministers.

The threatening activities include “intimidation, harassment and illegal activities occurring within your sovereign waters across the South China Sea,” he said at a meeting with defense ministers from the Association of Southeast Asian Nations. Worse, the aggression has been increasing in recent months, he said.

The remarks prompted a phone call from President Trump the same day and led Mr. Hegseth to dial back the criticism, apparently at the president’s urging, as the White House is in the midst of a concerted charm offensive aimed at improving trade and other relations with Beijing.

On his personal X account, Mr. Hegseth on Saturday stated: “I just spoke to President Trump, and we agree — the relationship between the United States and China has never been better.”

Mr. Trump’s meeting with Chinese President Xi Jinping in South Korea and Mr. Hegseth’s talks with Chinese Defense Minister Adm. Dong Jun in Malaysia have led to a new, less confrontational tone, he said.

“The admiral and I agree that peace, stability and good relations are the best path for our two great and strong countries. As President Trump said, his historic ‘G2 meeting’ set the tone for everlasting peace and success for the U.S. and China,” Mr. Hegseth said.

Mr. Hegseth said the War Department — the administration’s rechristening of the Defense Department that has yet to be formalized by Congress — will pursue a less confrontational approach under policies dubbed “peace through strength, mutual respect, and positive relations.”

Mr. Hegseth said he and Adm. Dong agreed to set up military-to-military channels “to deconflict and deescalate any problems that arise” and plan further meetings.

He ended the post with “God bless both China and the USA!”

During the ASEAN meeting, Mr. Hegseth criticized Chinese military attempts to coerce and threaten regional allies, including putting weapons on a disputed island that Beijing falsely declares to be a nature preserve.

“You don’t put [weapons] platforms on a nature preserve,” he said, calling the Chinese effort “yet another attempt to coerce new and advance territorial claims at your expense.”

Chinese provocations in the sea, he said, demonstrate a lack of respect for regional nations, “challenging and threatening territorial sovereignty.”