The price drop of 16.43% on Tuesday comes on top of a 6% fall before markets closed on Monday, after officials in New York (Frankfurt: A0DKRK - news) state released a report about the bank's alleged activities on behalf of so-called Iranian entities.
In early trading on Tuesday the loss peaked at more than 24% - temporarily wiping over £10bn from the bank's value.
The New York state department of financial services (DFS) has threatened to strip Standard Chartered of its right to operate in the state, saying the British bank hid $250bn (£160bn) in transactions tied to Iran, in violation of US law.
The DFS said the bank's "flagrantly deceptive actions" had left the US "vulnerable to terrorists, weapons dealers, drug kingpins and corrupt regimes".
The bank has strenuously denied the allegations, which include claims of stripping out identifying details of transactions concerning Iran.
"The group strongly rejects the position or the portrayal of facts as set out in the order issued by the DFS," Standard Chartered said in a statement, adding that it does "not believe the order issued by the DFS presents a full and accurate picture of the facts."
In its statement the bank also said it disclosed details of an internal review just days ago in its interim results, but that document says the review is still ongoing and therefore incomplete.
The interim result statement said: "As reported previously, the group is conducting a review of its historical US sanctions compliance and is discussing that review with US enforcement agencies and regulators."
Standard Chartered admitted: "The group cannot predict when this review and these discussions will be completed or what the outcome will be."
Investors reacted swiftly to the US claims, both in London and Hong Kong where its shares dropped by more than 20.6% - the biggest ever intra-day plunge.
Standard Chartered operates in 70 countries with a staff base of 87,000 people, and gains some 90% of its profits from emerging markets.
Monday's report comes exactly one month after the bank launched a global advertising campaign for TV, print, outdoor and digital to "reinforce the bank’s commitment to making a positive impact on the communities in which it operates".
In promotional literature the bank said: "We've operated for over 150 years in some of the world's fastest-growing markets. We aim to lead the way in Asia, Africa and the Middle East."
Seeking to maximise Asian and African interest in England's Premier League, the bank is a key sponsor of Liverpool Football Club.
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