JERUSALEM — One of Prime Minister Benjamin Netanyahu’s closest and longest-serving aides appeared ready to incriminate him on Wednesday after agreeing overnight to become a government witness, the latest twist in a spiraling graft scandal that seemed to dim Netanyahu’s legal and political chances of survival almost by the hour.

The fast-moving police inquiry into whether Netanyahu, already battling separate bribery allegations, had provided official favors to Israel’s largest telecommunications company, Bezeq, in exchange for fawning coverage on the company’s online news site prompted one member of the prime minister’s party to ask him to step aside and opposition politicians to call for early elections.

Netanyahu, who insists he has done nothing wrong, has faced corruption allegations periodically almost since first becoming prime minister in 1996. But the latest — with its suggestion of political payoffs to a company that bills ordinary Israeli voters every month — could prove the most damning. And as the revelations mounted, Israelis expressed increasing doubt about Netanyahu’s ability to maintain his grip on power.

“It was like watching a police car chase in pursuit of a robber on one of America’s endless highways,’’ columnist Sima Kadmon wrote in Wednesday’s Yedioth Ahronoth. “Riveting hours of dramatic and fateful revelations that are going to change not only the life of the man behind the wheel, but the face of our country.’’

The new state’s witness, ­Shlomo Filber, was director general of the Communications Ministry from 2015 until 2017, answering directly to Netanyahu, who at the time also held the title of communications minister. The ministry ruled or weighed in on a number of key regulatory decisions that provided enormous financial benefits to Bezeq and its controlling shareholder, Shaul Elovitch.

Filber, who was suspended from his post a few months ago as regulators from the Israel Securities Authority closed in, was arrested this week along with a number of other high-profile friends and confidants of Netanyahu, including ­Elovitch, members of his family, and other senior Bezeq executives.

Filber’s testimony promised to connect the two main arms of the Bezeq affair: the Communications Ministry’s dealings with the company and the decisions taken by editors at Walla, its online news subsidiary, according to a person with knowledge of the inquiry who was not authorized to speak about it publicly. In exchange, prosecutors agreed not to seek a prison sentence for Filber.

Such state’s witness agreements in Israel usually involve a criminal suspect giving up a bigger fish. Filber’s direct superior was Netanyahu.

Filber was expected to tell police that in his role at the ministry he was carrying out explicit and detailed instructions from Netanyahu, according to Israel’s Channel 2 evening news program, and that he came to realize he was being exploited.

Through a spokesman, ­Netanyahu responded: “It never happened.’’

In his first response to ­Filber’s agreement with prosecutors, Netanyahu projected bravado. He posted part of a biblical verse, Exodus 1:12, on his Facebook page: “But the more they were oppressed, the more they multiplied and spread.’’ Along with the verse, which refers to the Egyptians’ fear of the enslaved Israelites gaining strength, he included a chart from a survey by his own pollster, Geocartography, showing a spike in support for his conservative Likud Party.

The cases involving Netanyahu or his close associates have been piling up at a dizzying pace. Along with the developments in the Bezeq matter, which the police call Case 4000, were new suggestions that another of Netanyahu’s aides tried to bribe a judge to quash a criminal case involving his wife.

Netanyahu, who has described both sets of allegations as baseless and delusional, has not yet been named a suspect or called for questioning in either case.

But he is also deeply embroiled in two other corruption cases. One, known as Case 1000, involves accusations of illicit gifts for favors. In the other, Case 2000, he is accused of backroom dealing with the publisher of Yediot Ahronot, a major Israeli newspaper, for more favorable coverage. Police recommended last week that Netanyahu be prosecuted on charges of bribery, fraud, and breach of trust. Netanyahu denies any wrongdoing.

Any actual indictment may be months away, pending a hearing with Netanyahu’s lawyers and a decision by the attorney general.

Adding to the prime minister’s woes, however, Filber is not the first former ally to have turned against Netanyahu. Many analysts predicted as early as August that Netanyahu was doomed after police signed a state’s witness deal with Ari Harow, his former chief of staff and once one of his closest confidants, in Cases 1000 and 2000.