JERUSALEM (CNN) -- Israeli police investigators raided a ministerial building Tuesday and seized documents related to a fraud investigation of Prime Minister Ehud Olmert, a police spokesman said.
On Monday, police conducted a similar search of City Hall and other municipal offices in Jerusalem, taking documents as part of the ongoing inquiry.
The raid at the Ministry of Trade, Labor and Industry building comes as more than a dozen world leaders head to Israel, including President Bush, to celebrate the Jewish state's 60th anniversary.
Police are investigating whether Olmert received large sums of money illegally while he was mayor of Jerusalem and while he served as the nation's minister of industry, trade and labor. Olmert said last week that he has never taken a bribe but vowed to resign if he is indicted.
Police spokesman Micky Rosenfeld said Olmert received the questionable funds from 1993 through 2006, during his tenure as Jerusalem mayor and while he held several ministerial positions under former Prime Minister Ariel Sharon.
Olmert was also involved in the Likud Party primaries during that time, police said.
"It is suspected that the prime minister received significant sums of money from a foreigner or number of foreign individuals over an extended period of time, partly directly and partly indirectly," Israel police and the Ministry of Justice said in a written statement.
Olmert served as Jerusalem mayor from 1993 to 2003 and served in several ministerial capacities -- including as minister of trade, labor and industry -- from 2003 to 2006 before taking over as prime minister after Sharon was incapacitated by a stroke.
Also involved in the investigation is Morris Talansky, an American businessman who helped fund Olmert's election campaigns. Police questioned Talansky on Monday, according to the Israeli daily newspaper, Haaretz. Watch Talansky deny bribing Olmert »
He has denied that bribery was involved, and he told Israel's Channel 10 that he never thought any money he gave Olmert "was in any way illegal or wrong."
"He was not the only one that came to America to ask for money for their election campaign. And so I thought it was legal," Talansky said.
Talansky denied ever having a financial interest in Israel, saying he owned only an apartment in the country.
It is the fifth investigation of Olmert since he became prime minister two years ago and "the latest in a longer string of probes to dog him during his three decades in politics," according to Haaretz. Olmert has never been convicted of wrongdoing.
He is still under investigation for the purchase of a house in an upscale Jerusalem neighborhood he bought while he was the city's mayor. He allegedly purchased it below market value in return for favors.
Israeli officials also are investigating an alleged $10 million business deal involving his former business partner. Olmert is said to have taken part in the deal while he was labor minister.
He also is under investigation for allegedly appointing his cronies to positions in Israel's Small Business Authority from 2003 to 2006, while he was labor minister.
A year-long investigation into Olmert's role in the privatization of Israel's second-largest bank wrapped up in November with no charges filed against the prime minister.
Shula Zaken, Olmert's right-hand woman for 30 years, was suspended last year as head of the prime minister's office amid allegations she appointed her allies to Israel's Tax Authority. Olmert was not a suspect in the case but was questioned about Zaken's role.
Zaken refused to cooperate in the current investigation of Olmert. She has been placed under house arrest.
Olmert supporters maintain that the investigations are a political move by opponents who want him out of office.
Olmert has had dismal approval ratings since Israel's 2006 war with Hezbollah militants in Lebanon, which some analysts say failed to weaken the group either militarily or politically.