JERUSALEM - Prime Minister Benjamin Netanyahu underwent a new round of questioning on Friday over one of several graft cases that have threatened to topple him, Israeli media reported. The veteran premier's 12th round of questioning as a suspect in various cases comes two days before his wife Sara appears in court on charges of misusing state funds for catering at their official residence. Netanyahu has not been charged in any of the cases and a spokesman on Friday reasserted the prime minister's innocence. The prime minister has been repeatedly questioned over allegations involving Israeli telecoms giant Bezeq and its largest shareholder, Shaul Elovitch.

Netanyahu is accused of seeking favourable coverage from another Elovitch company, the Walla news site, in exchange for policies that could have benefited the mogul's interests to the tune of hundreds of millions of dollars.

He also faces interrogation as a witness in a case involving the purchase of three German submarines.

Israeli television on Friday showed footage of police officers arriving at his office.

Police confirmed the premier had been questioned for a number of hours, without giving further details.

Israeli media reported that Friday's questioning will for the first time cover two further cases in which he is suspected of corruption, fraud and breach of trust.

In one, he and family members are suspected of receiving around 1 million shekels ($275,000) worth of luxury cigars, bottles of champagne and jewellery in exchange for financial or personal favours.

In the second, he is suspected of seeking a deal for positive coverage from Israel's top-selling daily newspaper, Yediot Aharonot, in exchange for advancing a law that would have limited the circulation of Israel Hayom, a free competitor.

A spokesman for Netanyahu rejected the accusations: "It is now definitively clear that in the investigations against the prime minister, there is no meat on the bone, and that there is not even any bone at all."

"The prime minister has responded with confidence to the questions which have been posed to him, knowing that there was nothing and therefore there will be nothing" to come out of the investigations, the spokesman added in a statement.

Netanyahu's wife Sara is due to appear in court on Sunday charged with misusing state funds to buy catered meals costing $100,000 (85,000 euros) by falsely declaring there were no cooks available at the premier's official residence.

Prime minister for around 12 years in total and with no rival in sight, Netanyahu has maintained his innocence in all the cases.

But the investigations have gradually ratcheted up speculation over whether he will eventually be forced from office.

So far his coalition partners have stood by him despite the allegations. He is not obliged to step down as prime minister even if he is formally charged.