Bangladesh's central bank is unlikely to extend the contract of US cyber security firm FireEye to investigate the electronic theft of $81 million of its money, sources at the bank say, citing high costs as one of the factors.

Hackers who stole $81 million from Bangladesh's central bank have been linked to another cyber attack, this time on a bank in the Philippines, in addition to the 2014 hack on Sony Pictures Entertainment, cyber security company Symantec Corp says.

Bangladesh asks SWIFT to help its police question technicians sent by the global financial network to Dhaka to connect a new bank transaction system months before February's $81 million cyber heist, according to a source and an e-mail seen by Reuters today.

A government committee probing the Bangladesh Bank heist has held SWIFT responsible for weakening the payment system which allowed cyber thieves to steal $81 million from the central bank's account with the New York Fed.