According to sources, the central bank has received some complaints and is seeking preliminary information from the banks. In case the bank finds the problem to be serious, it may start a probe into the complaints.

However, some banks, including the foreign ones, sought to play down the problem saying it would not be easy to use ATMs for getting the forged notes into circulation. The ATMs can, according to them, ascertain the genuineness of the notes by testing the thickness of the currency.

While most of the nationalised banks are now setting up automatic teller machines in metro cities, foreign banks like Citibank and ANZ Grindlays bank took the lead in opening the onsite and offsite atms. Private banks like the Times Bank, Global TrustBank and ICICI Bank have also opened these outlets.

Almost all the ATMs installed have been imported with varying software according to the specific needs of the bank. ``RBI would like to know as to how these machines are working in a fool-proof manner in other parts of the world,'' sources said.

According to sources, the banks are trying to play down the problem to avert any panic situation. However, the RBI will seek comments and explanation of various banks, particularly those active in ATMs.