Nine more banks, including Lloyds Banking Group, have been issued with subpoenas by US state prosecutors as part of an expanding probe into allegations of attempts to manipulate the Libor rate.

According to the Wall Street Journal, the other banks sent subpoenas by the New York and Connecticut attorney-generals are Bank of America, Bank of Tokyo Mitsubishi UFJ, Credit Suisse, Rabobank, Royal Bank of Canada, Société Générale, The Norinchukin Bank and West LB.

The twin-headed investigation sees the nine banks join Barclays, Royal Bank of Scotland, HSBC, JP Morgan Chase, UBS, Deutsche Bank and Citigroup, which are already being probed by authorities.

Barclays, which confessed to manipulating Libor, duly coughed up a £290m fine as punishment and witnessed a series of high-level resignations such as chief executive Bob Diamond and chairman, Marcus Agius.