US banking giant Citigroup on Wednesday said it has fired 11 moreemployees over accounting fraud involving its Mexican subsidiary.Michael Corbat, Citigroup chief executive, announced the action taken at BancoNacional de Mexico (Banamex) in a memo to employees, saying the included fourmanaging directors, two of them in Mexico.The company earlier fired an employee who was believed to be "directly involved inthe fraud," he said.Corbat said that he expected that several other employees, "both inside and outsideof Mexico" may receive disciplinary action before the bank's internal investigationends.The New York-based bank found two cases of fraud at Banamex, which became partof Citi in 2001.According to Citi, Banamex extended credit to Oceanografia on the basis of bogusinvoices from the energy services company and to another company which it has notidentified.Both companies are sub-contractors of Mexico's state-run oil monopoly Pemex.The fraud is also under investigation by the US Securities and Exchange Commissionand the US Department of Justice."While the last few months have been difficult, Banamex is an institution with a rich,130-year history of providing exceptional banking services to its clients," Corbatsaid in the memo.Citi announced in February that it was slashing $235 million from its fourth-quarterand full-year 2013 financial results due to the recently discovered fraud.Corbat said it was more difficult to calculate the impact to the bank's credibility."Arguably, it is more damaging than the financial cost.