HSBC faces a deepening diplomatic crisis after US Secretary of State Mike Pompeo accused the bank of supporting the sanctioned leaders of a crackdown on dissent in Hong Kong.
Mr Pompeo claimed that Chinese officials have bullied HSBC into locking pro-democracy campaigners out of their accounts in the former British colony. At the same time, he said it is providing services to senior Communist figures on a White House blacklist.
There is no suggestion HSBC has broken American rules, which focus on banning financial transactions inside the US with 11 leading dignitaries in the Hong Kong and Chinese governments.
But the claims are still likely to spark serious concern at the bank, which was at risk of losing its crucial US dollar licence in 2012 after billions of dollars were laundered through its Mexico branch by drug cartels.
In a tweet, Mr Pompeo said: "The United States is dismayed to learn the Chinese Communist Party continues to bully our British friends and their corporate leaders.
"HSBC maintains accounts for individuals sanctioned for denying Hong Kongers’ freedom, while shutting accounts for those seeking freedom."
China has drawn condemnation from politicians and human rights activists around the world after introducing a law which effectively outlaws political dissent in Hong Kong. HSBC publicly backed the law, following warnings from senior regime figures that it could otherwise face reprisals.
Mr Pompeo's latest remarks were sparked by reports that executives at pro-democracy publisher Next Digital were unable to access their personal HSBC accounts or credit cards. Next Digital publishes Apple Daily and Next Magazine, two of Hong Kong's most popular titles.
Founder Jimmy Lai - an outspoken critic of Beijing - was arrested earlier this month under the new security law along with other executives and his two sons.
Mr Pompeo has previously warned that China's "browbeating" of HSBC was a "cautionary tale".
Expanding on his Twitter comments on Wednesday, Mr Pompeo said: "Only a few months ago, HSBC’s Asia-Pacific CEO signed a petition supporting Beijing’s decision to crush Hong Kong’s autonomy and its people’s freedoms.
"Free nations must ensure that corporate interests are not suborned by the Chinese Communist Party to aid its political repression."
The bank's Asia-Pacific boss Peter Wong signed a petition backing the law in June. It came after previous Hong Kong leader Leung Chun-ying warned the bank to bend its knee to the regime or face being locked out of the market.
Earlier this month, HSBC chief executive Noel Quinn suggested it could disown pro-democracy staff who are arrested in Hong Kong. He added that the lender follows the law in every country where it operates and that any action by authorities against its workers would have to be assessed on a case by case basis.
Washington also slapped fresh sanctions on 24 Chinese companies for building disputed outposts in the South China Sea.
HSBC relies on Hong Kong and mainland China for about 80pc of its profits, but a majority of its investors are based in the US and UK. A spokesman declined to comment.