A statement issued by Mr Olmert's office confirmed that police investigators would question him on Friday morning.

'Police have requested an investigation lasting one hour only. The prime minister has freed an hour from his busy schedule ... and the investigation will take place on Friday,' the statement read.

The legal source said Mr Olmert would be questioned about suspicions that when serving as a Cabinet minister he helped secure funding for a factory represented by his ex-law partner.

Mr Olmert has denied any wrongdoing.

He is the subject of two other corruption probes relating to his conduct before he became prime minister in 2006.

He is under criminal investigation, which he has described as 'needless', into accusations he dispensed favours in return for a discount on the 2004 purchase price of a Jerusalem home.

He is also being probed over allegations that as trade minister in 2003, he appointed cronies to a state business authority. He has said the suspicions are baseless.

Last November, police concluded there was insufficient evidence against him over his role in the sale of state-owned Bank Leumi when serving as finance minister. -- REUTERS