HSBC and Standard Chartered have been caught up in a US Justice Department probe into violations of sanctions on Iran.
The investigation has already led to a $80m (pounds 45m) penalty being paid by the Dutch bank ABN Amro which, along with Swiss giant UBS, has cut back its ties with Tehran under pressure from Washington.
The US government has been attempting to put pressure on Iran over its nuclear programme, which has been upgraded since the election in August last year of President Mahmoud Ahmadinejad.
The International Atomic Energy Agency is considering a call to report Iran to the United Nations Security Council over its nuclear programme. This could lead to wide-ranging sanctions being applied against the country. However, the US already has sanctions in place as against Iran, as well prohibitions against dealing with organisations it believes are involved in terrorism.
The Justice Department is investigating whether companies doing business with Iran might have broken those rules.
In 2004, the chairman of the US Senate Finance Committee, Charles Grassley, wrote to the Treasury Department asking whether three US corporations - GE, Halliburton and Conoco-Phillips - might be breaking sanctions. All three have reduced their operations in Iran.
A new line of investigation has focused on banking relationships. In December, ABN Amro paid $80m in penalties after it was found to have violated rules on dealing with Iran and Libya, while UBS paid $100m in 2004 after admitting breaches of rules on transactions with Iran, Libya, Cuba and Serbia. …