(Adds comments from Standard Chartered, Citibank)
ABUJA, Sept 6 (Reuters) - Nigeria's central bank has debited 2.4 billion naira ($7.9 million) in fines from Standard Chartered and 1.2 billion naira from Citigroup for allegedly helping South African telecoms firm MTN move funds abroad.
The central bank normally debits the account of banks when it imposes a fine or to implement aspects of its monetary policies such as cash reserve requirements.
The West African country's central bank last week ordered MTN and its lenders to return $8.134 billion it alleges MTN had sent abroad in breach of foreign exchange regulations.
MTN denies any wrongdoing, while Standard Chartered said it was fully co-operating with the central bank with a view to resolving the issue as soon as possible.
Citibank said in a statement it has sent a detailed response to the central bank addressing the allegations after the U.S. bank had received a letter imposing sanctions on it.
Nigeria's central bank fined Standard Chartered, Citibank, Stanbic IBTC Bank and Diamond Bank, for allegedly failing to verify that MTN had met all its foreign exchange rules.
Stanbic IBTC Bank, the local unit of South Africa's Standard Bank, was fined 1.8 billion naira and Diamond Bank 250 million naira.
Stanbic, said in a statement on Thursday that it had been debited by the central bank for the fine.
Standard Bank said in a statement to the Johannesburg stock exchange that it would continue to engage with the central bank despite the debit. ($1 = 305.20 naira) (Reporting by Chijioke Ohuocha, Paul Carsten and Alexis Akwagyiram Additional reporting by Tiisetso Motsoeneng in Johannesburg Editing by Kirsten Donovan and Alexander Smith)