Fake Indian currency notes of Rs 1,000 seized in Mumbai recently were unlikely to have been made in a small private press, a senior police official said on Friday.

"The quality of the notes was very good and they could not be made in a normal press which smaller groups of counterfeiters use," Additional Director General of Police (Anti-Terrorism Squad) K P Raghuvanshi said.

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The ATS chief, however, did not rule out a larger state-owned press in a neighbouring country being used to manufacture the notes, which were then sent here through smugglers.

ATS officials had arrested four persons on May 14 with fake currency with a face value of Rs 4 lakh (Rs 400,000).

The officials, who seized the currency, had been surprised by the detailing that had gone into the fake notes including the signature of a recent RBI governor.

"Normally the signature of the governor is that of one who had left some time back, but in this case they had the signature of the most recent governor. The details on the notes also very closely matched those on the original," ATS officials said.

According to police officials, the notes had failed to match the micro-lettering on the notes and the colouring on the '1000' written on the notes.

However, barring these minor errors, the quality of the paper and other details were almost completely accurate.

The case was subsequently transferred to the newly formed National Investigation Agency which is further investigating the case since the matter has possible international links.