Investigators on Monday questioned Israeli Prime Minister Benjamin Netanyahu over one of several graft cases that threaten to topple him, a police statement said.

Several Israeli media reports said the longtime premier was questioned at his official Jerusalem residence over a case of alleged corruption involving local telecoms giant Bezeq.

The reports said he could for the first time have faced questions over information provided by Nir Hefetz, a longtime Netanyahu aide who has turned state witness.

Netanyahu's wife Sara and son Yair were questioned separately at fraud squad headquarters near Tel Aviv, as was Shaul Elovitch, Bezeq's largest shareholder, media reported.

The police statement confirmed that the Netanyahus were interviewed by investigators from the national fraud squad and the Israel Securities Authority, without giving further details.

"The prime minister, his wife and son were questioned for a number of hours," it said.

"The investigation is being carried out under the supervision of the state attorney and with the approval of the attorney general."

This is the ninth time Netanyahu has been questioned in various cases directly or indirectly concerning him.

It was the first time Yair Netanyahu had been questioned, media reports said.

Netanyahu maintains he is innocent and has denounced allegations against him as a media and police witch hunt.

On February 13, police recommended he be indicted in two cases, though the attorney general has yet to decide whether to do so.

In the Bezeq case, Netanyahu is alleged to have sought favorable coverage from Elovitch's Walla news site in exchange for government policies that may have benefited the mogul's company by hundreds of millions of dollars.

Hefetz, a former spokesman for the Netanyahu family, agreed to turn state witness earlier this month, becoming the third former Netanyahu associate to cut such a deal in recent months.

Israeli media said he was believed to have been the intermediary between Netanyahu and Elovitch in the case.

Against the backdrop of the allegations, Netanyahu's government narrowly survived a crisis last month as rival parties in his coalition fought over conscription of ultra-Orthodox Jews into the army.

Critics accused Netanyahu of seeking to bring down the government to prompt fresh elections, with opinion polls showing his party likely to remain the largest in new elections.

So far his coalition partners have stood by him despite the allegations and Netanyahu is not obliged to step down even if officially charged.

However, Finance Minister Moshe Kahlon recently said if that were to occur he thinks the premier would have to resign or face being forced out by his coalition.

Monday's investigation was the first time the prime minister's son has been named as a suspect in the telecom case. Police did not offer details on their suspicions against the 26-year-old.

The investigation, dubbed Case 4,000 by police, has ensnared Netanyahu's former media advisor Nir Hefetz and former director general of the Communications Ministry Shlomo Filber. Both Hefetz and Filber have signed state's witness agreements and are providing evidence to police in the probe.

Netanyahu served as communications minister from November 2014 to February 2017.