Secretary of State Antony J. Blinken warned China on Tuesday that an “armed” attack against Philippine vessels in the South China Sea would trigger a mutual self-defense pact between Washington and Manila, a reflection of rising tensions in the region that risk dragging the United States into armed conflict with Beijing.

But in a sign that the United States hopes to de-escalate the situation, Mr. Blinken, on a visit to Manila, gave no indication that recent Chinese provocations — which include ramming Philippine vessels and blasting them with water cannons — crossed the threshold of “armed” attacks.

Pressed during a news conference alongside his Philippine counterpart on how to deter what some analysts call China’s “gray-zone coercion tactics,” which Philippine officials say include aiming a high-powered laser at a Philippine Coast Guard vessel and temporarily blinding some crew members, Mr. Blinken pointed to diplomatic, not military, measures.

“The very visibility of those actions, I think, has provoked from a number of other countries clear statements in support of the Philippines and against these provocative actions that are a threat to peace, security, freedom of navigation and basic rights under international law,” he said.

Mr. Blinken appeared to be attempting to strike a balance at a moment when the Biden administration is trying to sustain a recent thaw in relations with Beijing while also standing firm against Chinese territorial aggression in the region.

He was also signaling robust American support for the Philippines at a high-water moment for recent relations between the countries. Mr. Blinken met later in the day with the Philippine president, Ferdinand Marcos Jr., who has pivoted his country’s foreign policy back toward Washington since succeeding Rodrigo Duterte, who openly derided the United States and embraced Beijing.

President Biden hosted Mr. Marcos at the White House last spring, and Mr. Blinken is one of several top administration officials to visit the Philippines since Mr. Marcos’s May 2022 election.

The White House announced on Monday that Mr. Marcos would return to the White House on April 11, along with the Japanese prime minister, Fumio Kishida, for a joint summit — the first among the three nations. A statement from the White House press secretary hailed “the historic momentum in U.S.-Philippines relations.”

The U.S. sees economic as well as strategic benefit in the renewed friendship: The Philippines is one of seven countries to receive funding from the 2022 CHIPS act passed by Congress with President Biden’s support. The law authorizes new funding to boost American research and manufacturing of semiconductors and to diversify America’s high-technology supply chain.

During his stop through a muggy Manila, Mr. Blinken toured the local branch of an Arizona-based semiconductor company, calling the Philippines “an increasingly critical partner” in that effort.

But the threat of conflict with China looms over such positive talk.

The U.S. and the Philippines have been bound since 1951 by a mutual self-defense treaty, forged a decade after Japan conquered the nation, but which has now become a tripwire against Chinese claims to the South China Sea rejected by the United States.

The Chinese media noted Mr. Blinken’s visit here with scorn. The nationalist newspaper Global Times reported that “Washington’s use of Manila as a proxy to disrupt the South China Sea situation could bring regional strategic confrontation to an unprecedented level,” and accompanied its story with an unflattering photo of Mr. Blinken grimacing and furrowing his brow.

Global Times pointed a finger at Manila, accusing its forces of “illegally trespassing waters off China’s territory in the region and trying to mislead the international community on the issue.”

Mr. Blinken plans to travel on from the Philippines to the Middle East, with stops in Cairo, Egypt and Jeddah, Saudi Arabia. He said he would pursue efforts to broker a hostage deal between Israel and Hamas that would lead to a temporary cease-fire, the release of Israeli hostages and an influx of humanitarian aid into Gaza.

Mr. Blinken also intends to focus on postwar plans, including how to provide governance and security for Gaza once the fighting stops and “what is the right architecture for lasting regional peace” — a reference to U.S. efforts to broker a deal between Israel and Saudi Arabia that would establish normal diplomatic relations between the countries for the first time.