Nike Ching contributed to this report, which includes information from Reuters.

Revelations that China has been using social media accounts to influence public opinion on continuing protests in Hong Kong are reinforcing warnings from U.S. intelligence that the battle for information dominance has been joined.

Until now, much of the focus on been on Russia for its use of social media to meddle in a number of Western elections, including the 2016 U.S. presidential elections and, more recently, the 2018 congressional elections.

But top U.S. intelligence officials have repeatedly warned Russia is not alone, and that other U.S adversaries would be using lessons from Moscow's successes for their own purposes.

No adversary, they said, posed a bigger threat than China.

"The Chinese government uses all of the capabilities at their disposal to influence U.S. policies, spread propaganda, manipulate the media," former Director of National Intelligence Dan Coats said during a talk last September.

Around the same time, President Donald Trump began calling out China for placing ads and stories critical of the U.S.-China trade talks in regional newspapers.

China is actually placing propaganda ads in the Des Moines Register and other papers, made to look like news. That’s because we are beating them on Trade, opening markets, and the farmers will make a fortune when this is over! pic.twitter.com/ppdvTX7oz1 — Donald J. Trump (@realDonaldTrump) September 26, 2018

Such overt messaging through state media organs has long been a part of China's approach to trying to sway American opinion, unlike Russia's efforts targeting the U.S. in 2016, which involved the use of troll farms and numerous fake personas.

However, U.S. intelligence officials and some private sector analysts saw indications China was preparing to escalate its efforts. And less than three months later, the U.S. director of national intelligence sounded an additional alarm, accusing China, along with Russia, of actively meddling in the 2018 congressional elections.

Twitter, Facebook

This week, the world got another indication Beijing has intensified its efforts when Twitter announced Monday it had taken down 936 accounts "deliberately and specifically attempting to sow political discord" and undermine ongoing anti-government protests that have gripped Hong Kong.

I just came home from a completely peaceful march where possibly a million Hong Kong residents came out, with no police in sight, to call for basic democratic rights. What greets me is straight up lies from Xinhua about "bands of thugs", courtesy of Twitter advertising. pic.twitter.com/pUTsnqZ5oN — Pinboard (@Pinboard) August 18, 2019

Facebook soon followed, announcing it had removed seven pages, three groups and five accounts, all linked "to individuals associated with the Chinese government."

"This is some of the strongest evidence we have seen to date in public that the Chinese Party-state is engaged in influence operations on social media," said Samantha Hoffman, a research fellow at the Australian Strategic Policy Institute's International Cyber Policy Center. "I suspect that the evidence will continue to grow in the coming months."

Both Twitter and Facebook are blocked in China. Analysts pouring over the data released by both social media companies noted that some of the Twitter accounts had been active for years, some dating back to 2009, or earlier.

They note, though, that the accounts do not always appear to have done China's bidding.

"A number of these accounts move through numerous tools and many languages, switching after long breaks," Renee DiResta, a researcher with the Mozilla Information Trust Initiative, wrote on Twitter. "[It] Suggests at least some of the old/high-follower ones were purchased, or potentially rented."

China has yet to comment directly on the allegations by Twitter and Facebook. But Foreign Ministry spokesman Geng Shuang said Tuesday that the Chinese people and the media "have the right to express their point of view."

"What is happening in Hong Kong, and what the truth is, people will naturally have their own judgment," he added.

FILE - Chinese Foreign Ministry spokesperson Geng Shuang speaks during a press briefing in Beijing, July 11, 2017, in this image made from video.

U.S. reaction

There has also been little public reaction from U.S. officials, though many remain wary.

"This is another element of their efforts to manipulate data," Secretary of State Mike Pompeo told Fox News on Monday, asked about China's alleged activity on social media shortly after the news broke.

Others have tried to frame the influence campaign as another attempt by Beijing to distract the world's attention.

"The Chinese government chooses to blame the United States rather than address its own governance failures in Hong Kong," a senior administration official told VOA. "When a quarter of the population takes to the streets to voice their discontent, it's not because they were tricked into doing it."

Yet there is concern among intelligence officials and analysts that this use of social media shows that the Chinese Communist party, which already controls the information environment inside of China, is moving ambitiously to control the narrative fed to the outside world.

"This is a big deal because it's the first time that we've had confirmation of anything like this from any Western social media platforms," Matt Schrader, a China analyst at The Alliance for Securing Democracy at the German Marshall Fund, told VOA.

"You have to start asking, is China looking beyond Hong Kong? Is it looking beyond Taiwan? Is it practicing these tactics to be able to influence people globally?"