The ministry said: "The suspicions pertain mainly to Olmert's involvement in the investment center and political appointments, and helping his political friends in public bodies."
Olmert's office swiftly denied the allegations in a statement: "These are unnecessary investigations. It's clear beyond any doubt that the investigation will yield nothing."
The prime minister has been dogged by corruption allegations throughout his 30 year career in politics, but has never been convicted of any wrongdoing.
Last week, he was twice interrogated by police on suspicion he tried to rig the sale of Israel's second-largest bank in favour of two associates while he was finance minister.
He also is suspected of buying a Jerusalem home from a real estate developer at a substantial discount in return for helping the builder obtain construction permits from Jerusalem authorities.
Olmert has dismissed the various investigations as a political witch hunt.
But the probes have threatened to undermine him just as his public approval ratings have begun to rebound after last year's inconclusive war in Lebanon.