Standard Chartered has been accused of funnelling billions of dollars to the funders of terrorist groups such as Hamas and Hezbollah.
Court papers submitted by a whistleblower in the US allege that the British banking giant carried out more than $100bn (£78bn) of transactions between 2008 and 2013 with Iran-backed entities.
The alleged transactions form part of evidence provided by Julian Knight, a former Standard Chartered executive who wants the US government to bring a case against the bank.
Mr Knight alleges that previously undisclosed transactions reveal how Standard Chartered helped Iranian-linked terrorist groups on a larger scale than previously thought.
Standard Chartered, which is based in the UK but does most of its business abroad, was fined twice over its connections to Iran-linked transactions in 2012 and 2019 – but was never prosecuted.
The latest legal filing said: “Standard Chartered Bank (SCB) transacted with Iranian entities and foreign terrorist organisations for years after it claimed to have stopped.”
It added: “SCB facilitated many billions of dollars in banking transactions for Iran, numerous international terror groups, and the front companies for those groups.”
The filing alleges that the terror groups include Hamas, Hezbollah, the Taliban, and al-Qaeda.
According to the claim, the whistleblowers uncovered around 20,000 Iranian-related FX undisclosed transactions between 2008 and 2013, with a notional value of $100bn.
This comes after Standard Chartered paid $1.7bn in fines for money laundering last decade, ultimately avoiding criminal prosecution by the US authorities.
The Department of Justice dropped its probe into the bank in 2012, which came months after former chancellor George Osborne intervened on its behalf.
The latest raft of allegations forms part of an attempt by whistleblowers to revive a claim against Standard Chartered in the US.
A Standard Chartered spokesman said: “This filing is another attempt to use fabricated claims against the bank, following previous unsuccessful attempts.
“The false allegations underpinning it have been thoroughly discredited by the US authorities who undertook a comprehensive investigation into the claims and said they were ‘meritless’ and did not show any violations of US sanctions.
“We are confident the courts will reject these claims, as they have already done repeatedly.”