More than 100 police investigators raided government buildings and private offices Sunday, searching for evidence in a series of criminal investigations of Prime Minister Ehud Olmert.

The probes — all related to actions that took place before Olmert became prime minister — have threatened to weaken the Israeli leader at a time of growing momentum in peace efforts with the Palestinians.

The early-morning raid targeted more than 20 locations, including the Industry and Trade Ministry, the Postal Authority and Jerusalem's City Hall, said police spokesman Mickey Rosenfeld.

"Police investigators are searching a number of government and private offices in connection with three ongoing investigations" into Olmert, Rosenfeld said.

Investigators were still collecting evidence on Sunday afternoon, and the search was expected to possibly continue into early evening, he said.

He said authorities were expected to confiscate documents and other materials. He gave no further details.

Officials in Olmert's office declined comment. In the past, the prime minister has repeatedly denied any wrongdoing and has dismissed the investigations as a political witch hunt.

In one case, Olmert is suspected of buying a luxurious Jerusalem home at a substantial discount from a developer in exchange for arranging construction permits for the builder. Olmert is a former mayor of Jerusalem.

In a second case, police are looking into suspicions that Olmert acted improperly when he was trade minister earlier this decade. Authorities suspect Olmert steered a government grant to a friend and arranged improper political appointments.-

Olmert also is suspected of trying — albeit unsuccessfully — to rig the sale of Israel's second-largest bank in favor of two associates while he was finance minister in 2005.

Olmert has been dogged by corruption allegations throughout his three-decade career in politics, but has never been convicted of any wrongdoing.

Still, the probes have threatened to undermine him just as his public approval ratings have begun to rebound from last year's inconclusive war in Lebanon.

Olmert is preparing for a U.S.-hosted Mideast peace conference later this month in Annapolis, Maryland. He hopes the gathering will provide a launching pad for formal peace talks with the Palestinians after a seven-year lull.

A criminal indictment in any of the three investigations facing Olmert would deal a heavy blow to the peace efforts. Although Olmert would not be forced to step down, he would be seriously weakened and likely face heavy public pressure to step aside.