HO CHI MINH CITY, Vietnam — The Trump administration has told its senior diplomats in Vietnam not to take part in events marking the 50th anniversary of the end of the war.

Four U.S. officials who insisted on anonymity to describe sensitive diplomatic decision-making said Washington had recently directed senior diplomats — including Marc Knapper, the U.S. ambassador to Vietnam — to stay away from activities tied to the anniversary April 30.

That includes a hotel reception the day before, on Tuesday, with senior government leaders and an elaborate parade the next day — gatherings hosted by Vietnam in Ho Chi Minh City, also known as Saigon, where the war ended with South Vietnam’s surrender on April 30, 1975.

Veterans returning to Vietnam have also been told they’re on their own, for public discussions they organize on war and reconciliation, and anniversary events. For many, it amounts to a sudden reversal after months of anticipation.

“I really don’t understand it,” said John Terzano, a founder of the Vietnam Veterans of America Foundation who served two tours in Vietnam and has attended anniversary events for decades. “As a person who has dedicated his life to reconciliation and marveled at how it’s grown over the last 20 years or so, this is really a missed opportunity.

“It really doesn’t require anything of the United States to just stand there,” Terzano added, in an interview after landing in Hanoi. “This is all ceremonial stuff. That’s what makes it sound crazy and disappointing.”

State Department and embassy officials did not immediately respond to requests for comment.

A half-dozen people with knowledge of the directive said it was not clear where it originated or why it had been issued.

Wednesday, the anniversary, also will be the 100th day of Trump’s second term. Some U.S. officials speculated that a Trump appointee or a State Department leader feared drawing attention away from that milestone with events that might highlight America’s defeat in a war that Trump avoided.

In 1968, when 296,406 Americans were drafted into military service, Trump received a diagnosis of bone spurs in his heels that led to a medical exemption.

Regardless of the reasoning for Washington’s retreat from the 50th anniversary events, it adds another blow to decades of painstaking diplomacy by Republican and Democratic administrations, which had sought to heal the war’s wounds and build a strategic partnership for countering China.

Trump had already frozen U.S. Agency for International Development money allocated for addressing the legacy of the war. Even after officials restored some of it, many programs — for finding missing soldiers and demining old battlefields, for example — are still struggling with layoffs and uncertainty.

The foundation of bilateral relations, built by veterans from both sides, has essentially been weakened.

It was their emotional and physical hard work, with visits and civil society partnerships in Vietnam, that had persuaded former enemy governments to work through complicated issues like unexploded ordnance, soldiers missing in action, and the toxic legacy of Agent Orange and other American herbicides.

The momentum of postwar bonding led in 2023 to a new level of strategic partnership between the two nations. And the work had been on track to expand, until Trump’s approach to the world: pugilistic, strained relations and allergic to the acknowledgment of errors.

“It’s taken decades to build the current level of mutual trust and cooperation between the United States and Vietnam,” said George Black, the author of “The Long Reckoning,” a study of U.S.-Vietnam relations after the war. “And the whole process has been underpinned by our willingness to deal with the worst humanitarian legacies.”

Knapper, the son of a Vietnam veteran who was sworn in as the U.S. ambassador in 2022, had embraced his diplomatic mission. As of a few weeks ago, he had been expected to attend the main anniversary events next Tuesday and Wednesday alongside delegations from other countries, including Australia and the Netherlands.

He has often led ceremonies in which the United States gave artifacts from the war back to Vietnamese military families and repatriated the remains of what were believed to be missing Americans.

In an essay for this month’s Foreign Service Journal, he wrote about traveling to Vietnam with his father and son in 2004, describing the trip as “a clear reminder of the sacrifices on both sides and the enduring importance of reconciliation.”

“As ambassador,” he added, “I believe that to truly strengthen our ties, we must engage deeply and directly with the people and leaders of Vietnam.”

With that goal in mind, before Trump took office, the two countries had planned to show off their hard-earned bond in a new exhibit at the War Remnants Museum in Ho Chi Minh City.

The museum, Vietnam’s most visited cultural institution, chronicles American war atrocities. Under the plan, one of its wings was to be transformed: Design blueprints aimed for a lively introduction to the activists and officials who helped forge a model of postwar recovery.

Organizers had hoped the ambitious exhibit would open this month, or at least by July 11, the 30th anniversary of the restoration of America’s diplomatic relations with Vietnam.

But it’s now in limbo.

The project was funded by USAID, while the United States Institute of Peace managed the details. The Trump administration has dismantled both agencies.

Vietnamese officials did not respond to requests for comment about the anniversary. But they have repeatedly nudged the United States toward responsibility for the war’s lingering impact, with some success. After high-level discussions, the Defense Department recently restored money it had set aside for war legacy issues, even though its administrative partner, USAID, is gone.

As a result, the cleanup process for contamination from Agent Orange at the Bien Hoa air base has been revived, at least for this year.

Trump’s tariffs, however, have added another layer of vexation. With a rate set at 46% for Vietnam — above nearly every other country — some U.S. officials thought Vietnam might disinvite diplomats to the anniversary events.

That did not happen. The tariffs are now paused, and the two countries are locked in negotiations, with Vietnam seeking a reprieve and U.S. officials pushing Hanoi to decouple from China.