Turkish authorities were checking currency exchanges and cash dispenser machines on Thursday to help avert any damage from the circulation of counterfeit U.S. dollars, which has prompted a number of banks to stop accepting some of the bills.

The central bank said it was working with judicial authorities to address the counterfeiting issue and had shared a report and guidance with lenders after having examined the fake U.S. banknotes.

Though it was unclear how much counterfeit currency was in circulation across the country, several banking sources said that several foreign exchange offices and banks were no longer accepting some U.S. dollars.

A source with knowledge of the matter said there were no related problems with the financial system.

Several banking sources have said some $50 bills and $100 bills are suspected of being counterfeit and are not currently detected by money-counting machines.

The Turkish Banking Association said these machines as well as cash dispenser machines, or ATMs, were being checked and updated to halt any further circulation of counterfeit bills.

The source said a planned rapid system-wide update to money-counting machines would make detection possible.

Separately, a prosecutor's office in Istanbul launched an investigation into the issue, broadcaster NTV reported.