Israeli media say a close associate of Prime Minister Benjamin Netanyahu has agreed to testify against him in a bribery scandal.
Shlomo Filber was arrested on suspicion of promoting the interests of Israel's powerful telecom company in exchange for more positive news coverage of the prime minister.
Police have not confirmed that Filber has turned state's witness, but Netanyahu quickly denied any wrongdoing and described the allegations as a witch hunt, madness and lies.
The new revelations follow a police recommendation last week that Netanyahu should be indicted for bribery and fraud in two other corruption cases.
Opposition leaders like Tzipi Livni are calling on the Israeli leader to resign.
Livni said Netanyahu is corrupt and is so preoccupied with trying to save his political life that he cannot effectively govern.
But Netanyahu's right-wing coalition is standing behind him. Knesset member Yoav Kish of the ruling Likud party said unless there is an indictment, Netanyahu must be considered innocent until proven guilty.
The final decision on an indictment rests with the attorney general and could take months.
Netanyahu has been in office for nine years, but the latest developments have prompted many analysts to conclude that his days in power are numbered.