President Biden and Chinese President Xi Jinping met Monday in a virtual summit that featured no breakthroughs but enabled the two global superpowers to engage on a slew of sensitive issues that have strained ties — including Taiwan, trade and human rights.

In a 3½-hour conversation that the White House characterized as “respectful and straightforward and … open,” the two sides did not make pledges or depart from established positions. But the engagement was an acknowledgment that conflict, whether over trade or the South China Sea, can have grave repercussions around the world.

On that point, a senior Biden administration official said Biden raised with Xi the need for a set of strategic stability conversations around issues such as nuclear and hypersonic weapons, which China is developing at a pace that has alarmed defense officials. Biden raised concerns about China’s suppression of minorities in Xinjiang province, about unfair trade and economic practices and its recent aggression against Taiwan.

Xi, according to China’s central broadcaster, offered assurances that China, which has pledged to unify Taiwan with China by force if necessary, would do its “utmost” to achieve peaceful “reunification.”

The two leaders also discussed the existential nature of the climate crisis and the important roles played by their respective countries, the world’s top two emitters of greenhouse gases. They also talked about how they would continue this engagement in the future.

“As I said before, it seems to be our responsibility — as leaders of China and the United States — to ensure that the competition between our countries does not veer into conflict, whether intended or unintended,” Biden told Xi in brief remarks in front of reporters at the White House before the summit began. “Just simple, straightforward competition. It seems to me we need to establish a common-sense guardrail, to be clear and honest where we disagree and work together where our interests intersect, especially on vital global issues like climate change.”

Xi said ideological divides and blocs would bring “inevitable calamity” to the world. “The consequences of the Cold War are not far away,” he said.,He added that China was willing to hold dialogues on human rights issues “on the basis of mutual respect” but said Beijing would not support interference in its internal affairs, according to Xinhua News Agency, China’s official news service.

Xi also warned that China would take “decisive measures” against any moves to support Taiwan’s independence from China, whose ruling Chinese Communist Party has never governed Taiwan. “Such moves are extremely dangerous, just like playing with fire. Whoever plays with fire will get burned,” he said.

The discussion on Taiwan — perhaps the most fraught issue between the two countries — was “extended,” and Biden “clearly reaffirmed” the one-China policy acknowledging Beijing’s position that it is the sole legal government of China and related policy precepts, said a senior administration official, speaking on the condition of anonymity to describe the private summit. He also reminded Xi that as a senator he voted for the 1979 Taiwan Relations Act, and so, national security adviser Jake Sullivan said on Tuesday, “he understands deeply firsthand … that any effort to shape Taiwan other than peaceful means is of grave concern to the United States.”

The White House, in a statement, said the United States “strongly opposes unilateral efforts to change the status quo.” China has ramped up threats against Taiwan, flying sorties near the island and holding military exercises simulating attacks on the island that it views as a breakaway province. On Monday, hours before the meeting, Taiwan’s Ministry of Defense said China had sent six aircraft into its air defense zone. Taiwan sees itself as a sovereign state.

Recently, China also has conducted tests of hypersonic vehicles that have alarmed officials. And it has constructed hundreds of new missile silos and is building a new generation of strategic ballistic missile submarines.

Speaking on a Brookings Institution webcast Tuesday, Sullivan said that hypersonic and nuclear weapons are “sensitive and consequential issues that matter profoundly for America’s national security” and “how we effectively manage” those issues with China will be key.

He said Biden raised the need for strategic stability discussions and that they need “to be guided by the leaders.” He noted such talks would not be as mature as those that are ongoing with Russia, but it is “now incumbent on us to think about the most productive way to carry it forward from here.”

A former White House aide who handled China issues noted that the Obama administration conducted such talks with Beijing over nuclear, cyber and space issues. “We tried this several ways during the Obama administration and the Chinese just played for time and didn’t take it seriously,” said Evan Medeiros, who was a senior director for China under Obama. But since 2015, Xi has consolidated control over the military, and with China’s strategic weapons buildup, he said, new talks should be tried.

Though the talks were long and wide-ranging, at least two potentially thorny topics did not arise, said the senior administration official., One was the 2022 Winter Olympics in Beijing, which is the subject of calls for diplomatic boycotts to protest China’s alleged human rights abuses. Another was the issue of China not granting visas for U.S. journalists, after expelling more than a dozen American reporters last year in what Beijing said was retaliation for Washington imposing restrictions on its journalists.

After the summit, the state-run China Daily, citing unnamed sources in China’s foreign ministry, said the two sides had reached an agreement before the meeting to ease restrictions on journalists from each other’s countries and begin processing visas.

Trade was raised, and Biden emphasized the need for China to uphold its commitments to buy additional goods from the United States, but it was not a “dominant part” of the conversation, the official said.

Overall, the White House sought to frame the relationship as one of “steady state” competition in which the lines of communication remain open, while the United States works with allies and partners, as the official said, “to confront China where we need to” and work together where “our interests … intersect.”

In an earlier briefing for reporters, the official said “unlike previous approaches to policy with respect to China, the Biden administration is not trying to change China through bilateral engagement … Rather we are trying to shape the international environment in a way that is favorable to us and our allies and partners.”

Biden and Xi also discussed the coronavirus and broader health security issues, including the importance of bringing an end to the pandemic, and the role of vaccines, the official said. They also exchanged views on the upcoming discussions around Iran’s potential return to nuclear talks.

White House press secretary Jen Psaki told reporters Monday that Biden was going into the meeting “from a position of strength,” especially compared with shortly after he took office.

She touted Biden’s sweeping $1.2 trillion infrastructure measure — a campaign promise that he signed into law Monday on the White House South Lawn — noting that it marks the first time in 20 years that the United States “will be investing more in infrastructure than China, and that is going to strengthen our competition at home, in addition to putting millions of people to work.”

She also pointed to Biden’s recent trip abroad — to the Group of 20 summit in Rome and the U.N. climate summit in Glasgow, Scotland — as an example of the president’s strategy for handling China through building the United States’ global alliances, especially with European partners.

“We have made enormous strides in building those relationships, including on the president’s trip just two weeks ago, where he had a range of conversations,” Psaki said.

Other top administration officials held multiple conversations with their Chinese counterparts to prepare for the summit. On Saturday, for instance, Secretary of State Antony Blinken pressed Wang Yi, the Chinese foreign minister, on rising tensions over Taiwan, expressing in a call concerns about Beijing’s “continued military, diplomatic and economic pressure” against the self-governing island.

Yet the United States and China have found common cause on climate, with the two countries pledging last week at the U.N. climate summit in Glasgow to work together on slowing global warming.

The Chinese president recently tightened his grip on power in Beijing with a new resolution that bolsters his position, allowing him to stay in his role until at least 2027 — a development that U.S. officials said made the direct discussion between Biden and Xi on Monday all the more critical.

The meeting began Monday almost exactly on schedule, at 7:46 p.m. Eastern time and ended at 11:24 p.m. The two communicated via interpreters. Although they were not physically in the same room, they were able to “interact with one another in the way that they’ve not quite had in their phone calls,” the senior administration official said.

Among the Chinese officials calling in from the Great Hall of the People in Beijing were Wang, economics czar and trade negotiator Liu He and senior diplomat Yang Jiechi, as well as Vice Foreign Minister Xie Feng and Ding Xuexiang, director of the general office of the Central Committee of the Chinese Communist Party, a top political body, who is considered part of Xi’s inner circle. Biden administration attendees included Blinken, Sullivan and Treasury Secretary Janet L. Yellen.

Monday’s virtual meeting marked the third direct conversation since Biden took office in January; the last two discussions were over the phone, most recently on Sept. 9. Xi has not left China since the start of the coronavirus pandemic.

The relationship between the two men stretches back nearly a decade, to when Biden was vice president under President Barack Obama. Psaki stressed that the leaders’ rapport allows Biden “a level of candor, to be direct, not to hold back.”

Still, Psaki made clear that the relationship has its limits. In 2013, during a trip that Biden took to Asia, Xi welcomed the U.S. vice president as “my old friend” — a descriptor Biden rejected when asked about it in June, noting pointedly: “Let’s get something straight. We know each other well; we’re not old friends. It’s just pure business.”

Asked Monday about Biden’s June assessment, Psaki said she could confirm that the president “still does not consider him an old friend, so that remains consistent.”

Yet as the summit began, Xi seemed determined to reiterate his camaraderie with Biden — reviving what, depending on one’s perspective, is either a term of endearment or an unwelcome moniker.

“Good to see you, Mr. President and your colleagues,” Xi said, through an interpreter. “It’s the first time for us to meet virtually. Although it’s not as good as a face-to-face meeting, I’m very happy to see my old friend.”

Lily Kuo reported from Taipei.