NEW YORK (Reuters) - The U.S. Department of Justice and Citigroup Inc said on Monday that they have settled a criminal investigation into violations of anti-money laundering rules and the Bank Secrecy Act at the bank's Banamex USA unit. The settlement includes a non-prosecution agreement and a forfeiture by Citigroup of $97 million, the department and the bank said in separate statements. The bank said it had it already reserved for the expense. Under the agreement, Banamex USA admitted criminally failing to maintain an effective anti-money launder program, the DOJ said. Between 2010 and 2012, Banamex USA conducted fewer than 10 investigations on more than 18,000 alerts generated by its monitoring system for some $142 million in potentially suspicious transactions, the department added. The agreement follows a 2015 settlement by Citigroup for $140 million with the Federal Deposit Insurance Corp and the California Department of Business Oversight over evidence of Bank Secrecy Act violations by Banamex USA. After that settlement, Citigroup said it would liquidate what was left of Banamex USA, which had some branches in the United States and was affiliated with Citigroup's Mexico City-based Banamex subsidiary, now known as Citibanamex. Banamex USA is expected to finally cease banking operations as of June 30, Citigroup said in its statement on Monday. (Reporting by David Henry in New York; Editing by Chizu Nomiyama and W Simon)