China has been buying up ads on U.S. social-media sites and adopting online tactics reminiscent of Russian disinformation campaigns in an apparent attempt to shape the story internationally about the coronavirus response, according to researchers analyzing the activity.

The efforts include ad purchases on Facebook Inc. promoting the English-language arms of Chinese state-media outlets, as well as posts there and on Twitter Inc.’s platform that in some cases disparage U.S. efforts to fight the global pandemic, the researchers say.

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From mid-February until early March, social-media sites linked to Chinese state media posted more than 3,300 times a day, triple the normal rate, according to Recorded Future, a Somerville, Mass.-based cybersecurity consulting firm. Those outlets were principally active on Facebook and Twitter, the research showed.

The Chinese tweets, researchers say, evoke Russia’s tactics, which involved spreading messages that can incite doubt and stir anger about basic facts and sometimes promote fictitious claims. Russia also leaned heavily on state media to spread its message online.

The Chinese Foreign Ministry didn’t respond to a request for comment, and Russia has denied spreading disinformation.

The Chinese ad spending accelerates a broader social-media effort—which got a boost during last year’s Hong Kong protests—to shape opinion about China in the English-speaking world, researchers said.

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China has bought more than 200 political ads on Facebook since the end of 2018, but more than a third have been purchased in the past two months, said Vanessa Molter, a researcher at the Stanford Internet Observatory, a cyber-policy institute. Most of the recent ads focused on trying to shape global perception around China’s handling of the coronavirus outbreak, she said.

This story continues in The Wall Street Journal.