Israeli Fraud Squad detectives Friday questioned Prime Minister Ehud Olmert for the seventh time in recent weeks over corruption affairs the premier is suspected of being involved in.

Olmert's artist wife Aliza was also quizzed during the lengthy session which, as with previous interrogations of the prime minister, went on for longer than scheduled.

Police did not immediately release details of the interrogation, but Israeli media reported that the focus was on a Jerusalem house in an upscale neighbourhood, which Olmert is suspected at buying for far below the market price in return for helping the building contractor receive construction permits form the Jerusalem authorities.

Prior to Friday's round of questioning, Israeli media also speculated that the detectives would focus on political appointments Olmert made, in contravention of Israeli law, when he served as minister of trade and industry before he became prime minister.

Previous rounds of questioning undergone by Olmert centered on accusations that that in the years before he became prime minister he received hundreds of thousands of dollars, most of it via envelopes full of cash, from US-Jewish fundraiser Morris Talansky.

He has also been questioned regarding suspicions that he double-, and even triple-, billed sponsors for overseas visits, and used the extra money to pay for trips for his family, and that as trade and industry minister pushed for favourable responses to be given to grant applications submitted to the ministry's investment centre by clients of his former law partner.

Olmert has denied all the accusations against him, and although he admitted receiving funds via Talansky in what has become known as "the money envelopes" affair, denies the sums mentioned, and insists it was legitimate reimbursements for food and accommodation.

Despite media reports, usually quoting anonymous police sources, that an indictment will be issued in the coming weeks, it remains unclear if and when Olmert will formally be charged with the various offences he is accused of committing.

But the ongoing investigations have nonetheless further eroded the premier's already low popularity and last month he announced that he intends stepping down from the premiership after his Kadima party chooses a new leader in primaries on September 17.

Announcing his intentions in a televised appearance, he slammed the conduct of the investigations against him, saying that while he was proud to live in a country "where the prime minister can be investigated like any other citizen," he had "been denied the elementary right to the presumption of innocence."

Olmert's office has been involved in a public spat with the police and the state prosecutor's office regarding leaks from the investigations against him.

Accounts of police interrogations of witnesses and others involved in the alleged scandals have sometimes appeared in the media within a very short time of their having taken place.

Olmert became prime minister in March 2006, after he led the Kadima party to victory in Israel's Knesset parliamentary elections. His parliamentary career stretches back to 1974. As a novice legislator he made a name for himself by battling organized crime.