Prime Minister Benjamin Netanyahu is facing a new police investigation into fresh claims that he received funds from abroad.
No other information has yet emerged about the probe which, according to two of Israel's most prominent investigative journalists, has been going on for at least a month. No official source has confirmed its existence.
Mr Netanyahu responded that the reports were "complete nonsense".
Legal sources said that unlike previous investigations into Mr Netanyahu's affairs and those of other senior politicians, during which leaks abounded, this case is expected to be very different.
The investigators, Attorney-General Avichai Mendelblitt and national police chief Ronny Alsheikh, have ordered a zero-tolerance policy towards leaks.
Mr Mendelblitt is already deliberating over three other major decisions regarding Mr Netanyahu and his wife Sarah.
He must decide whether the donation made to Mr Netanyahu by French businessman Arnaud Mimran, now on trial in Paris for fraud, warrants a criminal investigation; whether the funding for Mr Netanyahu's trips abroad a decade ago constitute illegal payments; and whether to charge Mrs Netanyahu for alleged misuse of public funds.
To get more Israel news, click here to sign up for our free Israel Briefing newsletter.