HONG KONG (NYTIMES) - Jenny Lee, 26, marched with a friend through the sweltering streets of Hong Kong the other day, hoisting an American flag over her shoulder. "We hold this to tell the world that we want democracy and freedom," she explained.

The authorities in China, however, are holding up those kinds of gestures as evidence of what Chinese officials portray as a US campaign to orchestrate the protests that have roiled Hong Kong for almost three months.

China's increasingly caustic accusations against the United States - in state media and official statements - reflect a deepening conviction that support for democratic rights in Hong Kong is part of a broader effort to undermine the Communist Party.

"It's their bete noire: democracy and democratic values," said Professor Jean-Pierre Cabestan of Hong Kong Baptist University and the author of China Tomorrow: Democracy Or Dictatorship?

"The goal is to erase them from Hong Kong."

There has been no concrete evidence that the protests are anything but what demonstrators say they are: a largely leaderless upwelling of frustration and resistance to the mainland's encroaching control of Hong Kong's affairs.

But Chinese officials now point to a pattern of US actions that they say amounts to foreign interference, even collusion.

Some of the accusations amount to little more than crude disinformation, but others are grounded in just enough fact to spin a conspiracy theory of covert US nefariousness, intended to loosen the Chinese leader Xi Jinping's authoritarian grip on power.

They include statements of support for the protests from congressional leaders and Democratic presidential candidates, and meetings between Hong Kong opposition figures and administration officials.

One such meeting with a diplomat in the US Consulate in Hong Kong has been seized on by China, as was another in Washington with Vice-President Mike Pence and President Donald Trump's national security adviser, Mr John Bolton.

China's liaison office in Hong Kong on Monday, for example, vehemently denounced a relatively mild, bipartisan statement by the chairman and a ranking member of the House Foreign Relations Committee, Mr Eliot Engel and Mr Michael McCaul, that expressed support for the protests and called on both sides "to refrain from violence and seek a peaceful accommodation".

A spokesman for the Chinese office replied in a statement that the two men "have ignored the facts, turned black into white, harboured evil intentions and nakedly interfered in Hong Kong affairs and China's internal affairs".

China has a long history of blaming "foreign forces" for challenges it has faced internally, including the Tiananmen Square protests 30 years ago.

But the depth and ferocity of China's accusations over Hong Kong suggest they are not merely propaganda intended for domestic or international audiences.

Instead, analysts said, they reflect the thinking of an increasingly anxious leadership that sees any manifestation of popular sentiment in the streets as a potential "colour revolution" like those that swept Georgia, Ukraine and later the Arab world.

A 42-page report released recently by China's Ministry of Foreign Affairs singled out the National Endowment for Democracy, the congressionally funded organisation founded in 1983 to support the spread of democracy and human rights around the world, accusing it of underwriting a similar revolution in Hong Kong.

"The US is not satisfied in overt oral support for Hong Kong but resorts to financial backing," the state English-language television network, CGTN, wrote with inexact grammar in an article posted on its website and included in the ministry's report. The article went on to argue that the endowment acted in concert with the CIA "in covert actions against governments".

The Chinese have denounced the US activity not only publicly but also privately in meetings with their American counterparts, according to officials in both countries.

China is also angrily pushing back against international criticism. A spokesman for China's Foreign Ministry, Mr Geng Shuang, denounced a statement by the Group of Seven leaders last week calling on both sides to avoid violence in Hong Kong.

He accused the seven nations - Britain, Canada, France, Germany, Italy, Japan and the United States - of "harbouring ulterior motives".

He also declared moot the 1984 declaration between Britain, then Hong Kong's colonial ruler, and China that established the framework for Hong Kong as a special autonomous region, with rights not extended to Chinese citizens on the mainland.

That declaration serves as a congressionally mandated benchmark for US relations with Hong Kong and China under the Hong Kong Policy Act, enacted as law in 1992. The State Department is required by law each year to evaluate the extent of Hong Kong's autonomy.

"The tempo of mainland central government intervention in Hong Kong affairs - and actions by the Hong Kong government consistent with mainland direction - increased, accelerating negative trends seen in previous periods," the latest report, issued in March, warned.

The Trump administration has reacted inconsistently to the protests. Mr Trump, focused principally on the trade tensions with China, once dismissed the protests, calling them an internal matter.

Others in the administration have spoken out more forcefully, however, and the protests have galvanised support across the political spectrum in Washington.

And that has given the Chinese fodder for their arguments. After initially ignoring the protests, officials have begun to respond to US statements more directly, while turning up the propaganda against the US in state media, which has been strikingly effective at shaping public opinion on the mainland.

The report on CGTN cited "more American faces" appearing at rallies. One of those that have drawn attention belongs to Mr Mark Simon, a top aide to Mr Jimmy Lai, the Hong Kong media tycoon whom China loves to hate. Mr Simon, a veteran of the US Navy, helped set up the meeting between Mr Lai and Mr Pence in July that prompted an official diplomatic protest.

Mr Simon said that he had long helped Mr Lai to make donations to civic organisations in Hong Kong, but he emphasised that he had no ties to US intelligence and played no role in the protests, despite insinuations to that effect.

"It's just ridiculous that a big, fat white guy is running the show in Hong Kong as a CIA handler," he said.

On the streets, Hong Kong's protesters have also mocked China's accusations, saying they were intended to belittle their grievances.

Ms Phoebe Chan, who accompanied her American flag-carrying friend, Ms Lee, ridiculed Chinese media reports that protesters were being paid to participate. "We are coming out on our own," she said.

If anything, protesters like her would like to see the US get more involved. She cited the special trade status that Hong Kong receives under US law, which officials in Washington have warned could be revoked if China were to crack down with force. "This is our hope," she said.