The latest accusation, announced in a joint statement by the Ministry of Justice and the police, is that Olmert billed multiple charitable organizations for the same flights, and then used the extra money to fund personal vacations during his tenure as mayor of Jerusalem and trade minister. In addition to billing the organizations, Olmert would also bill the government, the statement said.

The organizations included groups that help soldiers, mentally disabled children and the physically handicapped, according to sources close to the investigation. They also included the Holocaust memorial Yad Vashem, which operates under a state charter.

The statement said that a travel agency coordinated the fraud on Olmert's behalf. Olmert would speak to various groups during trips abroad and then ask each one to separately pay the air fare, according to the statement. A source close to the investigation said Olmert pocketed in excess of $100,000.

The allegations come in the aftermath of testimony by New York businessman Morris Talansky that he gave Olmert $150,000, much of it in cash, over a nearly 15-year period. Talansky said he believed Olmert used the money to fund a lavish lifestyle - including a family vacation in Italy and fancy cigars.

A spokesman for Olmert yesterday said the prime minister would continue fighting the allegations.

"The prime minister is convinced that he has done nothing wrong and that as this investigation continues, his innocence will clearly be shown," said Mark Regev, Olmert's spokesman.

Olmert has said he will step down if he is indicted, and investigators indicated yesterday that they were nearing that point. Olmert was questioned by investigators for two hours yesterday.

The prime minister is facing political pressure from allies to step aside. Those allies include his top lieutenants in government - Defense Minister Ehud Barak and Foreign Minister Tzipi Livni - both of whom covet Olmert's job. Livni is expected to seek the leadership of Olmert's Kadima party when primaries are held next month.

Olmert has not said whether he plans to run, and political analysts said yesterday's development makes it highly unlikely.

"Before, there was an assumption that he could last until the end of 2008," said Menachem Hofnung, a political scientist at the Hebrew University in Jerusalem. "Now the question is whether he can last until the end of July. Olmert for all practical purposes is finished."

Hofnung said the new allegations "look serious. It appears to be a very simple and ugly fraud."

If Olmert does resign, it could lead to new elections, and stall U.S.-backed efforts to reach a peace agreement between Israel and the Palestinian Authority by the end of the year. Olmert has also opened negotiations with Syria, which could be jeopardized by a change in government.