US millionaire businessman Morris Talansky who authorities suspect of illegally funding Israeli Prime Minister Ehud Olmert will testify in the investigation on May 25, public radio reported Wednesday.

Talansky will give sworn evidence before a judge in a closed-door session and then be allowed to return to his home in the United States, the radio said.

Anti-fraud police are seeking to establish whether Olmert had given any favours in exchange for alleged illegal funds he received from Talansky in the 13 years before he became premier in 2006.

Olmert's lawyers have appealed the decision to summon Talansky as a witness.

Olmert, who has been dogged by scandals since he took office in 2006, last week insisted he had never taken a bribe and said he would quit if charges were pressed.

But he acknowledged that he had received what he said were legitimate financial contributions for various election campaigns from Talansky.

Talansky said on Sunday that he gave financial contributions to Olmert but insisted he believed they were intended for legitimate purposes.

"I never thought in any way that the money I gave was illegal or wrong," the 75-year-old Jewish financier told Israel's private Channel 10 television in his first public comments on the scandal.

Police have also questioned two other US businessmen, Sheldon Edelson, a property and casino tycoon, and Daniel Abraham, who is linked to a different investigation into Olmert's affairs.

According to the liberal Haaretz newspaper, police suspect Olmert had asked Edelson and Abraham to purchase minibar refrigerators for their hotels made by a company in which Talansky had a stake at the time.