Israel's attorney-general is investigating allegations that Prime Minister Ehud Olmert accepted bribes as acting finance minister last year.
No formal charges have ever been made against Mr Olmert
The allegations - on an Israeli website - say he took the bribes during a major bank privatisation deal.
Mr Olmert denies any wrongdoing. He has faced other corruption inquiries but no formal charges have been filed.
This is the latest in a series of allegations of wrongdoing by senior political figures in Israel.
"At this stage no decisions have been taken, no criminal procedure is being taken [against Mr Olmert] and Israel's police is not involved in the issue," the justice ministry said in a statement.
The President, Moshe Katsav, is being investigated over allegations of sexual harassment, while former Justice Minister, Haim Ramon, and a former Environment Minister, Tzahi Hanegbi, are both facing charges for misconduct.
All have denied doing anything improper.
The latest investigation into Mr Olmert's dealings centres on the privatisation in 2005 of Bank Leumi, Israel's second largest.
An Israeli website, News First Class, has alleged that as finance minister at the time, Mr Olmert tried to help two overseas-based businessmen who were bidding for the bank.
A controlling interest in the bank was eventually bought by a US investment group to which the businessmen were unconnected.
The Israeli Justice Ministry released a statement in which it said its investigation was specifically "in response to reporters' queries after the report on the Web site News First Class".
Israel's government watchdog, the State Comptroller's Office, is already investigating Mr Olmert's sale in 2004 of a property in Jerusalem to a political supporter.
It is alleged that the apartment was sold at an inflated price.
The State Comptroller's Office has also recommended a criminal investigation into appointments made in 2004 when Mr Olmert was trade and industry minister.