The United States has an “ironclad” alliance with the Philippines, U.S. Defense Secretary Ash Carter said on Thursday, countering statements by the southeast Asian nation’s president that have thrown bilateral relations into deepening uncertainty.

Carter spoke a day after Philippine President Rodrigo Duterte, who has branded President Barack Obama a “son of a bitch,” declared upcoming U.S.-Philipppines military exercises “the last” and ruled out any joint navy patrols.

“As it has been for decades, our alliance with the Philippines is ironclad,” said Carter, speaking to American sailors aboard the U.S.S. Carl Vinson at its home port in San Diego.

Through a “landmark” recent agreement, “the United States is supporting the modernization of the Philippine Armed Forces,” he said.

Duterte has engaged in near-daily outbursts against the United States for the last month, raising questions about whether Manila’s next moves could complicate regional diplomacy.

Among other measures, the firebrand leader has said he will order the pullout of the remaining U.S. special forces stationed in the Philippines’ restive south.

The comments have cast doubt over an alliance that both countries have sought to strengthen amid shared concerns about China’s military clout and pursuit of broad maritime claims. The Philippines and China have long sparred over sovereignty in the South China Sea.

Carter also noted the Maritime Security Initiative, under which the United States is providing tens of millions of dollars to the Philippines.

Despite his inflammatory comments, Duterte has said the Philippines will maintain security agreements with Washington, and Philippines Foreign Secretary Perfecto Yasay said Duterte had only ruled out joint patrols beyond the Philippines’ 12-nautical mile territorial waters. U.S. officials said this week that they had not seen formal requests from the Philippines to stop the joint patrols.

Carter also spoke broadly about the U.S. “rebalance” toward the Asia-Pacific region, and touted strong bilateral relationships with countries in the area, including Thailand, Japan, South Korea, and Australia.

Carter is due to host defense ministers from southeast Asian countries in Hawaii this week, including the Philippines. Such gatherings have recently been dominated by China’s claims on parts of the South China Sea. Vietnam, Malaysia, Brunei, the Philippines and Taiwan have rival claims.

In a visit to the Philippines in April, Carter announced expanded military ties, including regular rotations of U.S. troops and military equipment and joint patrols in the South China Sea.