Jerusalem (CNN) Israeli Prime Minister Benjamin Netanyahu was interrogated Friday by police for a third time as part of an ongoing graft probe, a source close to Netanyahu said. The source spoke to CNN anonymously because he was not allowed to speak with the media.

The earlier two interrogations , carried out at the Prime Minister's residence in Jerusalem, lasted a total of eight hours.

Netanyahu has repeatedly denied the accusations, calling them "nothing." On Thursday, he responded angrily on his Facebook page, saying, "The cat's out of the bag. Pressure from the media and politicians on the Attorney General and law enforcement so that they issue an indictment at any cost against the Prime Minister. This is an attempt to overthrow the government in an undemocratic way."

The preliminary examination of Netanyahu began last summer, but it wasn't until about two months ago that the attorney general believed there was enough evidence to launch the criminal investigations.

Since his first interrogation in early January, Netanyahu has been questioned "under caution," meaning he is suspected of having committed a crime. So far, investigators have interviewed dozens of witnesses, including some outside Israel.

Netanyahu took questions from other politicians while speaking Wednesday in a session of the Knesset, Israel's Parliament. He directed his anger at the opposition. "My friends on the left -- I have news for you: I will continue to lead the state of Israel for many years to come -- for the citizens of Israel, for the state of Israel and for the Jewish people -- and you better start getting used to it," he said.

Israeli politicians in the opposition have called for an open and thorough investigation; some have demanded that Netanyahu step down.

Isaac Herzog, leader of the Zionist Union Party and head of the opposition, criticized the Israeli leader on Facebook following Wednesday's Knesset session.

"Instead of answering our questions, the Prime Minister chose to offer a collective response at the end of the discussion, where he, as usual, scolded the media and the Left, who (he says) are trying to bring him down through false investigations. Actually, it was not clear who exactly Netanyahu blames, it sounds like he blames everyone, everyone except for Netanyahu. This was my answer to Netanyahu's performance, " Herzog said.

Israeli police Chief Roni Alsheikh told reporters this week that police are nearing the conclusion of their investigation and will issue their recommendation regarding an indictment within the next few weeks. If police recommend indicting Netanyahu, then the attorney general must decide on whether to file charges.

Under Israeli law, Netanyahu is required to resign only if he is convicted of having committed a crime and the conviction is upheld through the appeals process all the way to Israel's High Court. But if he were indicted, he would face tremendous public and political pressure to step down.

Netanyahu has been the subject of earlier criminal investigations. In his first term as Prime Minister in the late '90s, police recommended indicting Netanyahu on fraud and breach of trust, but the attorney general declined to file charges, saying there wasn't enough evidence.