HANOI — The United States is rescinding a decades-old ban on arms sales to Vietnam, President Obama said at a news conference in Hanoi on Monday, ending one of the last legal vestiges of the Vietnam War.

The United States has long made lifting the embargo contingent on Vietnam’s improving its human rights record, and recently administration officials had hinted that the ban could be removed partly in response to China’s buildup in the South China Sea.

But Obama portrayed the decision as part of the long process of normalizing relations between the two countries after the Vietnam War.

“The decision to lift the ban was not based on China or any other considerations,’’ he said, with the Vietnamese president, Tran Dai Quang, standing stiffly by his side. “It was based on our desire to complete what has been a lengthy process of moving toward normalization with Vietnam.’’

Obama insisted that the move should not be interpreted as carte blanche for weapons sales to Vietnam and that the United States would review future arms sales to “examine what’s appropriate and what’s not,’’ as it does with any country.

“We’re going to continue to engage in the case-by-case evaluation of these sales,’’ Obama said. “But what we do not have is a ban that is based on an ideological division between our two sides.’’

As for human rights, he said, “this is an area where we still have differences.’’

Human rights advocates, who had asked Obama to hold off on lifting the ban until Vietnam had released some prominent political prisoners and promised to stop the police beatings of protesters, condemned the decision.

“President Obama just gave Vietnam a reward that they don’t deserve,’’ said John Sifton, the Asia policy director of Human Rights Watch.

Quang defended his country’s rights record.

“The consistent position and viewpoint of the Vietnamese government is to protect and promote human rights,’’ he said, adding, “those achievements have been highly recognized and appreciated by the international community.’’

US officials portrayed lifting the embargo as part of a strategy to help Vietnam defend itself against an increasing threat from China in the South China Sea. Analysts have speculated that in return, Vietnam would grant the United States access to the deepwater port at Cam Ranh Bay.

While there were no statements about such a deal on Monday, Obama did announce commercial deals worth more than $16 billion, including one in which Boeing will sell 100 aircraft and Pratt & Whitney will sell 135 advanced aircraft engines to VietJet, a privately owned low-cost airline.

Obama said that improved ties with Vietnam made sense for the United States, since it was a fast-growing country in one of the fastest-growing regions of the world.

He predicted that the Trans-Pacific Partnership, a trade deal among 12 nations that has very little chance of passing Congress before the election in November but that would benefit Vietnam greatly, would someday become law.

“I remain confident we’re going to get it done, and the reason I remain confident is because it’s the right thing to do,’’ he said, acknowledging that “the politics will be noisy.’’

All three remaining presidential candidates in the United States — Donald Trump for the Republicans and Hillary Clinton and Bernie Sanders for the Democrats — oppose the pact.

Obama’s trip to Vietnam is part of an effort by this Southeast Asian nation to recalibrate its relationship with China, its giant neighbor in the north. China remains Vietnam’s largest trading partner and an ideological ally, but the two countries have sparred over Beijing’s claims of waters off Vietnam’s coast in the South China Sea.

The United States has sought to challenge those maritime claims, as well as others contested by Japan and the Philippines, both US allies.

Since 2014, when China placed an oil rig in waters near the Paracel Islands, which Vietnam claims, Hanoi has repeatedly asked Washington for the freedom to buy US lethal weapons. The United States partly relaxed the ban two years ago, allowing the purchase of nonlethal equipment for maritime defense.

China’s reaction to the decision on Monday was subdued.

“The arms embargo is a product of the Cold War and should never have existed,’’ Hua Chunying, a spokeswoman for the Foreign Ministry, said during a regular news briefing in Beijing. “We welcome normal relations between Vietnam and the United States.’’

But beneath the polite response are deep concerns in Beijing about the intentions of Vietnam. And Vietnam, while seeking to defend itself from China, is unlikely to completely sever itself from China’s orbit.

Obama also announced on Monday that the two sides had formalized an agreement to allow the opening of Fulbright University Vietnam in Ho Chi Minh City, the first independent university in Vietnam in which the government will have no role in creating the curriculum or teaching students.

The university’s chairman, Bob Kerrey, a Vietnam veteran and a former senator of Nebraska, said the school may start teaching undergraduates in the fall of 2017.

Obama also said that for the first time, Peace Corps volunteers will be posted to Vietnam.

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