Seven banks have been issued subpoenas in the US for their alleged manipulation of the Libor interbank lending rate.
New York Attorney General Eric Schneiderman and Connecticut Attorney General George Jepsen are jointly investigating alleged manipulation of the London interbank offered rate by lenders.
According to Bloomberg, they have requested information from JP Morgan Chase, Barclays, Royal Bank of Scotland, HSBC, UBS, Deutsche Bank and Citigroup as the investigation looks set to widen.
Barclays was fined over £290m by US and UK regulators in June for its manipulation of the Libor and Euribor interbank lending rates, a move which has seen a number of senior staff resign from the firm.
Following the Barclays fine, US regulators said they were investigating a number of other banks for potential Libor rigging. In the UK, the Serious Fraud Office has also said it will investigate a number of institutions over the manipulation of Libor.
The Government has ordered a review into Libor, which is currently being undertaken by Financial Conduct Authority chief executive designate Martin Wheatley.
Last month, research from Morgan Stanley revealed that as many as 12 banks caught up in the Libor rate-rigging scandal could face combined regulatory fines of more than £14bn.
Morgan Stanley said the estimated fines would cut between 4 and 13 per cent off banks’ earnings per share for 2012. The research also assumes that most of the other 11 banks will admit to similar behaviour but will not receive the discount Barclays received for early co-operation. The report says Royal Bank of Scotland is likely to face one of the biggest fines with Deutsche Bank also likely to be hit.