Lawmakers lambasted TikTok’s chief executive about the platform’s ties to China in a roughly five-hour hearing on Thursday, punctuating how the viral video app has become a prime battleground as the United States and China compete for tech leadership.

Shou Chew, the chief executive of TikTok, which is owned by Chinese internet giant ByteDance, was barraged with questions about the app’s relationship to its parent company and China’s potential influence over the platform. Republican and Democratic lawmakers repeatedly asked Mr. Chew if TikTok was spying on Americans on behalf of the Chinese government, cut him off midsentence and angrily demanded “yes” or “no” answers from him.

The hearing, which was a rare display of bipartisan unity and was harsher in tone than previous congressional hearings featuring American executives of social media companies, was complicated by Chinese authorities weighing in. Hours before Mr. Chew testified, China’s commerce ministry said it opposed a sale of TikTok, in a public rebuke of the Biden administration, which has demanded the divestiture and threatened a possible U.S. ban of the app.

That left Mr. Chew, 40, in a difficult position as he struggled to cast TikTok as an independent company that wasn’t influenced by China. “ByteDance is not owned or controlled by the Chinese government,” he said at one point, a response that visibly frustrated lawmakers. “It is a private company.”

The hearing and China’s statement cemented how TikTok has become a focal point of geopolitical tensions between the United States and China. President Biden and the Chinese leader, Xi Jinping, are both campaigning to bolster their own technology sectors and have cut off trade to each other’s countries as suspicions between Washington and Beijing have mounted.

With the United States and China at odds over a TikTok sale, there are basically two paths for the app in the United States. The Biden administration could force a ban of the app, which could run into a difficult court challenge, or it could revisit negotiations for a technical fix to data security concerns.

“The future of TikTok in the U.S. is definitely dimmer and more uncertain today than it was yesterday,” said Lindsay Gorman, head of technology and geopolitics at the German Marshall Fund and a former tech adviser for the Biden administration. “It’s not just one side of the aisle clamoring for TikTok to address these national security concerns, but this is now coming from all sides.”

To continue operating in the United States without changing its Chinese ownership, TikTok had proposed ways to protect American users by walling off their data, among other steps. But no security agreement has been reached and U.S. intelligence officials have warned that the app may be an arm of the Chinese government to spy on Americans and to spread propaganda.

The stakes heightened in recent weeks, with the Biden administration pushing for TikTok to be sold off from its Chinese owners or face a possible ban on American soil. But China’s comments on Thursday against a sale narrows what the White House can potentially do to contain the app without escalating tensions, leading to acrimonious exchanges at the hearing with Mr. Chew.

It is rare for chief executives of foreign-owned companies to testify in Congress, with one of the last times being when Toyota’s president appeared in 2010 to discuss the recalls of millions of cars.

The bipartisan unity at the hearing was striking, with Republicans and Democrats at odds on issues from federal spending to abortion rights. August Pfluger, a Republican lawmaker from Texas, told Mr. Chew that the chief executive had inspired bipartisan support that hadn’t been seen in three or four years.

Over the past few years, lawmakers have increasingly coalesced around the growing animus against Chinese businesses in the United States, with government bans on exports to Chinese telecommunications companies and several bills that aim to limit TikTok and other technologies tied to hostile foreign governments.

At the hearing, more than 50 lawmakers expressed deep skepticism of Mr. Chew’s defense. They portrayed TikTok as a danger to national security, accusing it of invading people’s privacy, harming the mental health of teenagers and leading to the deaths of some young people.

“We do not trust TikTok will ever embrace American values,” said Cathy McMorris Rodgers, a Republican of Washington and the chair of the House Energy and Commerce Committee, which held the hearing. “TikTok has repeatedly chosen the path for more control, more surveillance and more manipulation. Your platform should be banned.”

In a statement, a TikTok spokeswoman said the hearing “was dominated by political grandstanding.”

Mr. Chew tried distancing TikTok from China, stressing that he was born in Singapore and that he lives there with his wife, who was born in Virginia, and two children. He emphasized early on that he attended business school in the United States.

But he acknowledged that he reports directly to ByteDance’s chief executive, Liang Rubo, and that some TikTok employees participate in ByteDance’s incentive plans for stock options.

Mr. Chew argued that banning the app would be a strike against free expression. TikTok serves many small businesses and creators who make their living from selling goods and through sponsorships on the app. He said the app had 150 million U.S. users and 7,000 employees in the country.

He also repeatedly pointed to efforts to protect the data of Americans. The company came up with a plan, Project Texas, to store the data of American users on domestic servers run by the Texas-based software giant, Oracle. He insisted that the data security program, which the Biden administration has rejected, would be the best way to protect consumers.

“The bottom line is this: American data is stored on American soil by an American company overseen by American personnel,” Mr. Chew said.

But lawmakers remained skeptical. Several brought up China’s declaration that it would oppose TikTok’s sale, saying it was evidence of the country’s influence over the company. They cited reports of ByteDance’s surveillance of American journalists as proof of the company’s abuse of privacy and user security. In December, TikTok said that China-based ByteDance employees had retrieved the sensitive data of U.S. TikTok users, including reporters, to try to find who was leaking internal information to journalists.

“I’m not convinced that the benefits outweigh the risks that it poses to Americans in its present form,” Frank Pallone, the ranking Democrat of New Jersey, said of TikTok. “The combination of TikTok’s Beijing communist-based China ownership and its popularity exacerbates its danger to our country and to our privacy.”

Concerns over TikTok increased during the Trump administration. In 2020, President Donald J. Trump tried, unsuccessfully, to ban TikTok from Apple’s and Google’s app stores unless it was sold to an American buyer. A deal to sell stakes in the app to Oracle and Walmart never came together.

After the Biden administration came into office, it initially focused on negotiating the security deal that would allow TikTok to keep operating in the United States. That changed in recent weeks with the White House’s demand that TikTok’s Chinese owners sell the app. The administration also backed a new bill that would give it more power to ban TikTok.

The bill, sponsored by Senators Mark Warner, Democrat of Virginia, and John Thune, Republican of South Dakota, would give the Commerce Department the power to ban any app or service that could endanger national security of the United States.

Mr. Chew, who was appointed TikTok’s chief executive in May 2021, has in recent months embarked on a charm offensive in Washington, meeting with lawmakers, think tank leaders and journalists. This week, he tried garnering support with his own video on TikTok’s official account, warning users that politicians “could take TikTok away from all 150 million of you.”

TikTok has support from free speech proponents, who warned against a ban of the app.

“Banning or restricting access to social media is a hallmark of authoritarian regimes, and we should be very wary about giving the U.S. government that kind of power,” Jameel Jaffer, executive director at the Knight First Amendment Institute at Columbia University, said in a statement.

Lawmakers also raised concerns about TikTok and young Americans in the hearing. The app is used by 67 percent of U.S. teenagers, according to the Pew Research Center. TikTok has faced criticism that it’s too addictive and that its algorithm can bombard teens with videos that put them in dangerous and even lethal situations.

“TikTok could be designed to minimize the harm to kids, but a decision was made to aggressively addict kids in the name of profits,” Representative Kathy Castor, Democrat of Florida, said during the hearing.

Mr. Chew said that TikTok had worked to limit the repetition of videos about topics like extreme exercise and that the app’s guidelines did not allow content promoting self-harm or eating disorders. He also pointed to new 60-minute screen time limits, which parents can control, for users 12 and under, and prompts that now appear after 60 minutes for 13- to 17-year-olds.

Lawmakers weren’t assuaged. Representative Lisa Blunt Rochester, Democrat of Delaware, said Mr. Chew’s testimony solidified concerns over the company’s ties to China, data privacy violations and how the app treats children.

“I think that really summarizes why you see so much bipartisan consensus and concerns about your company,” she said. “And I imagine that it’s not going away anytime soon.”

Chang Che contributed reporting.