SINGAPORE — Defense Secretary Jim Mattis arrived in this Asian metropolis Friday, preparing to address nations in the region as they grapple with the growing threat of North Korea, Chinese militarization in the South China Sea and a rebellion in the Philippines that now includes links to the Islamic State.

The trip, Mattis’s second to Asia since becoming defense secretary in January, will include a speech Saturday during the Shangri-La Dialogue, a defense summit, and smaller meetings with counterparts from Japan, South Korea and other nations. Mattis will emphasize how Washington is “broadening and deepening” its relationships in the region, said David F. Helvey, a senior adviser on Asia issues who is traveling with Mattis.

The trip builds on months of Mattis reassuring allies, and it comes with a new complication: President Trump pulling out of the international Paris agreement stemming climate change Thursday. The issue is considered especially important in Asia, where the Pacific Ocean dominates life, violent storms are common and several megacities are along coastlines.

The Pentagon has labeled climate change as a threat to national security for years, and Mattis testified in January during his confirmation process that it required a “broader, whole-of-government response.” He was not among the Cabinet secretaries whose comments the White House released Thursday in support of Trump’s decision.

The secretary, who has advocated the need for the United States to maintain alliances and keep the promises it makes, declined to be interviewed by reporters traveling with him Wednesday and Thursday. In a statement distributed to media on his plane, he said that he will emphasize U.S. intentions to “stand with Asia-Pacific allies and partners, reinforcing the international order necessary to secure a peaceful and prosperous and free Asia.”

Mattis’s trip coincides with the U.S. Navy launching a multiday operation off the coast of the Korean Peninsula in which two Navy aircraft carriers and their associated strike groups are training together. The Pentagon has characterized the so-called dual-carrier operation as routine, but acknowledges that nothing like it has occurred near the peninsula in about 20 years.

Helvey said the operations, which include the carriers USS Ronald Reagan based in Japan and the USS Carl Vinson of San Diego, are meant to reassure allies, “show resolve” and keep the U.S. military ready for whatever it needs to do.

He added, however, that he did not view the carrier operations as provocative. It’s also unlikely that they will deter North Korea from continuing to test intercontinental ballistic missiles and nuclear weapons, he acknowledged.

The Trump administration has enlisted the help of China, a major trade partner with Pyongyang, to put pressure on North Korea to change its behavior. Helvey said it is not clear if that will work, but that the United States expects China and other countries in the region to lean on North Korea to change its behavior.

“We’ll continue to support that diplomatic effort until we’re told otherwise,” Helvey said.

At the same time, Washington is grappling with how to respond to China claiming international waters in the South China Sea as its own and building man-made islands and infrastructure apparently designed for military use.

U.S. officials have said that the United States can continue to disapprove of the militarization of the South China Sea while asking Beijing for help on North Korea.

“Our concern in the South China Sea certainly hasn’t diminished,” Helvey said. “We would oppose any action that would infringe upon the fundamental principle of freedom of navigation.”

China, South Korea and the United States also are grappling with what to do about a defensive missile system that the United States deployed in the fall to South Korea in response to North Korean threats. China has protested the deployment given its proximity to their own territory, and South Korean President Moon Jae-in recently said they were not aware that there are more than two launchers in the system, and pledged to investigate.

Helvey said that the United States was transparent with the government in Seoul through discussions, and that a full missile battery — known formally as Terminal High Altitude Area Defense, or THAAD — includes six launchers.

In the Philippines, the United States is monitoring and discussing a recent resurgence in radical Islamist violence on the southern island of Mindanao. Some of the militants are said to be foreign fighters from Malaysia and Indonesia and have pledged loyalty to the Islamic State, which the Trump administration has promised to “annihilate” wherever it is.

The United States has long had a Special Operations mission devoted to training and advising Philippine authorities to deal with the rebels, but cut it back from more than 300 troops to about 100 in 2014. It isn’t yet clear whether the Pentagon would escalate it again, but Helvey said that right now they are not discussing doing so.

“We’ll obviously get the input and recommendations from the commanders in the field,” he said. “And then the secretary will make a recommendation on if and how we do any adjustments to that. But you know, whether or not we do that is a hypothetical that I’m not going to entertain at this point.”

Last month, Philippine President Rodrigo Duterte declared martial law on Mindanao. In recent days, Philippine forces there have engaged in combat with militants, forcing civilians to flee or hide in their homes. A friendly-fire airstrike also killed several Philippine troops during the fighting.