When members of Congress grilled TikTok’s chief executive last month on Capitol Hill, the app’s supporters sprang to its defense online. The lawmakers were “old, tech-illiterate,” one said. “Out of touch, paranoid and self-righteous,” said another. The hourslong hearing “destroyed the illusion that US leads in cyber era,” read another post. These particular barbs did not come from TikTok’s users — 150 million and counting in the United States — but from representatives of China’s government. In an information campaign primarily run on Twitter, Chinese officials and state media organizations widely mocked the United States in the days before and after the hearing, accusing lawmakers of hypocrisy and even xenophobia for targeting the popular app, according to a report released on Thursday by the Alliance for Securing Democracy, a nonpartisan initiative from the German Marshall Fund. TikTok, which is owned by the Chinese technology company ByteDance, has sought to assure American lawmakers that it is independent from China’s influence, and that it has extensive plans for securing Americans’ data and providing oversight of its content recommendations. Shou Chew, TikTok’s chief executive, explicitly said at the House hearing that ByteDance was “not owned or controlled by the Chinese government.” China’s information push, however, showed just how deeply invested Beijing was in the company’s fate. Just hours before Mr. Chew’s testimony last month, China’s Commerce Ministry said it opposed a sale of TikTok in a direct rebuke of the Biden administration, which is pushing a sale. Chinese officials “clearly feel a stake in it,” said Michael H. Posner, a former assistant secretary of state and now director of the Center for Business and Human Rights at the Stern School of Business at New York University. The report from the Alliance for Securing Democracy found that Twitter accounts from Chinese diplomats and state media outlets posted nearly 200 tweets about TikTok in the week around the congressional hearing on March 23. That compared with fewer than 150 posts in all of January and February. Chinese state media accounts also ran more than 30 stories about TikTok in outlets like China Daily, the report said. The researchers said in an interview that they had found similar content on Facebook and YouTube. Asked about its support for TikTok, China’s foreign ministry said it opposed American actions that violate market principles and rules under the World Trade Organization to target foreign companies. “What the US should do is to stop smearing and slandering, and provide a fair, just, open, and nondiscriminatory business environment for companies from all over the world,” the statement said. China’s effort has echoes of its defense of another Chinese company that has found itself in the cross hairs of American legal and political controversy: Huawei, the telecommunications giant, which the United States has identified as a potential national security threat. The scale and tone of China’s criticism of the US government have intensified, though, reflecting the sharp deterioration of relations between the two countries despite a halting effort last year by President Biden and the Chinese leader, Xi Jinping, to reverse the decline. “This is how the US talks to the world,” a spokeswoman for China’s Ministry of Foreign Affairs, Hua Chunying, wrote last month on Twitter, in English, with the hashtag #TikTokHearing. Her post, which was retweeted more than 1,200 times, included a clip from TikTok showing Representative Kat Cammack, Republican of Florida, who during the hearing called the app “an extension” of the Communist Party of China. When Mr. Chew asked for a chance to respond, Representative Cathy McMorris Rodgers, Republican of Washington and the chair of the House Energy and Commerce Committee, said it was time to move on. “What I think is surprising is how direct the attacks against US lawmakers were,” said Etienne Soula, a research analyst at the Alliance for Securing Democracy who wrote the report with Lindsay Gorman. “It’s par for the course for them to go after the US system in general, saying it’s dysfunctional, that democracy doesn’t work and that it’s not a real democracy.” It is far less common, he added, to see “very open insults.” Chinese officials, including diplomats around the globe, have become adept at using social media — including platforms like Twitter and Facebook that are banned in China — to spread their political views to an international audience. The latest campaign, however, sought to directly influence the political debate in the United States. Posts by officials and state media mocked the political process. At least one stoked speculation of a potential “Gen Z rebellion” if lawmakers or the administration succeeded in banning the app or forcing its sale, as the Biden administration had been proposing. “China is careful not to interfere with other countries’ internal affairs or internal politics, so to have them weigh in so openly to encourage voters to riot — it’s outside the ordinary,” Mr. Soula said. Other posts compared tense photos of the roughly five-hour hearing with pictures of Apple’s chief executive, Tim Cook, who was visiting China around the same time and smiling and posing with locals. “Isn’t it clear which side supports free trade and which side is against it?” said a post from the Twitter account of Global Times, a nationalist paper owned by the Communist Party. Still others sought to deflect attention from TikTok, asking why lawmakers were highlighting its risks to young people while “doing nothing on gun-control legislation.” They also called the criticism of the app “xenophobic.” (TikTok’s chief operating officer has also said calls to ban the app are xenophobic.) More recently, Chinese state media outlets have continued to push the campaign on their Twitter accounts, with China Daily posting an article on March 31 titled: “US says China can spy with TikTok. It spies on world with Google.’” On TikTok itself, many users also rallied behind the company and Mr. Chew, who has become an unexpected celebrity. The hashtag #TikTokBan has been viewed more than two billion times. Brooke Oberwetter, a spokeswoman for TikTok, said Mr. Chew’s popularity on the platform had increased organically. The Alliance for Securing Democracy did not track Chinese propaganda on TikTok’s service as part of the report. Several Chinese media outlets already have accounts on the app. Their accounts and videos are identified with labels that say “China state-controlled media,” and their profiles have fewer followers than they do on Twitter, suggesting that the latter remains the principal platform for China’s global messaging. “We label state-affiliated media so our community is clear if they are engaging with content that may be controlled or influenced by a government,” Ms. Oberwetter said. “This is an ongoing process, and we’ll continue to review new accounts and add labels as and when they join the platform.” CGTN, the English-language channel of the Chinese state television network, posted a TikTok video on March 24 that featured defenses of the platform from some of the influencers the company flew to Washington to help defend it before the hearing. “When it comes to hot-button topics involving autocratic actors, it can be difficult to tell the difference between organic arguments and arguments derived from autocratic propaganda, even in open, democratic information spaces,” the Alliance for Securing Democracy said in its report. “Should geopolitical debates occur on Chinese-owned social media platforms like TikTok going forward, it could become even more difficult to differentiate between organic arguments and propaganda.” The potential to shape public opinion is one of the major security concerns that American intelligence officials have raised about TikTok. “If there are 150 million US users, and God knows how many in the rest of the world,” Mr. Posner said “it’s a platform for disinformation just waiting to be exercised.”