Israel's government watchdog announced on Thursday he would investigate Prime Minister Benjamin Netanyahu amid accusations private businessmen paid for lavish trips for him and his family.
State Comptroller Micha Lindenstrauss said he would probe whether the funding for the trips did not "contravene accepted norms of conflict of interest for ministers."
He also said he would look into funding Netanyahu received during the primaries of his Likud party.
The investigation comes after a report last week on the private television station Channel 10 accused Netanyahu of having tens of thousands of dollars worth of private flights, luxury hotels and meals for himself, his wife and children paid for by wealthy foreign benefactors.
The alleged incidents occurred when Netanyahu was an MP and cabinet minister and do not relate to his premiership.
On Wednesday Netanyahu filed a libel suit against Channel 10 and the Maariv daily seeking damages of one million shekels ($282,000/202,000 euros) from each, saying many of the facts reported were false and aimed to "ridicule" and "humiliate" him.
In a rare interview Thursday, Netanyahu's wife Sara described the allegations as "rubbish and lies" and said people were trying to target her husband through her.
"It's easier to harm him through me," she told Channel 2 news. "It's a repetitive narrative."
Sara Netanyahu has been at the centre of several controversies in recent years, including allegations she meddled in appointments in his office and mistreated household staff.
Following the initial broadcast, Netanyahu released a statement saying the report was part of a long-standing campaign by the Channel 10 reporter "to besmirch the name of the Prime Minister and his family.
"No external body ever paid for Mr Netanyahu's children's flights at any point when he was in public office," it said.
Netanyahu's predecessor, Ehud Olmert, resigned under pressure in September 2008 after police recommended that he be indicted for corruption, and he is currently on trial on three counts of fraud and bribery.
In one case, he is accused of unlawfully accepting gifts of cash-stuffed envelopes from Jewish-American businessman Morris Talanski and of multiple-billing for foreign trips.
And the justice ministry said earlier this month that prosecutors will file charges against 18 people, including Olmert, for allegedly taking bribes in a massive property scandal.