A close aide to Israel's Prime Minister Benjamin Netanyahu has agreed to testify against him in one of several corruption cases, Israeli media report.
Schlomo Filber is said to have turned state's witness in what is being seen as a blow to the PM.
Mr Netanyahu is alleged to have pressed regulators so as to help the Bezeq telecoms giant in return for favourable news coverage from one of its websites.
He denies all corruption allegations, saying they are a political witch hunt.
Mr Filber is credited with helping Mr Netanyahu win the last general election and was appointed by him to head the communications ministry.
Mr Filber, who was arrested on Sunday and is being held with Bezeq executives, told Israeli police on Wednesday that he received explicit instructions from Mr Netanyahu to help Bezeq, Haaretz reports.
For his part, Mr Netanyahu says all decisions about Bezeq were transparent and subject to oversight.
Police have declined to comment officially on reports that Mr Filber has turned state's witness.
Last week, police said there was enough evidence to indict Mr Netanyahu for bribery, fraud and breach of trust in two other cases.
It is now up to the attorney general's office to decide whether to prosecute, but a decision may not emerge for months.
In one case, the PM is alleged to have asked the publisher of an Israeli newspaper, Yediot Aharonot, for positive coverage in exchange for help in reining in a rival publication.
Police said the editor of Yediot Aharonot, Arnon Mozes, should also face charges, but his lawyers say it will become clear that he committed no criminal offence.
And the second case centres on a claim that Mr Netanyahu received gifts worth at least a million shekels ($283,000; £204,000) from Hollywood mogul Arnon Milchan and other supporters.
Police allege that Mr Netanyahu, having received the gifts, pushed for the Milchan Law, which would have ensured that Israelis who return to live in Israel from abroad are exempt from paying taxes for 10 years.
Israeli police say Mr Milchan could face bribery charges, but his legal team have dismissed any suggestion of bribery, saying his friendship with Mr Netanyahu pre-dates the time he held a government position.
Mr Netanyahu has dismissed these allegations too, calling them "baseless" and saying he was certain the truth would be revealed.
The conservative premier, who is 68, has been in power since 2009 and faces elections in 2019.
If the reports about Mr Filber are confirmed, this would be the first time one of Mr Netanyahu's inner circle has agreed to testify against him.