A former defense minister called Israeli Prime Minister Benjamin Netanyahu "corrupt" on Thursday and said he should resign over a possible conflict of interest related to the purchase of German submarines.

Moshe Yaalon, an outspoken critic of Netanyahu's government, told Channel 10 TV that as defense minister he was sidelined from the deal, which went ahead after Netanyahu replaced him last year.

He said he was "convinced" Netanyahu should resign over the affair. Later in the interview, he said "it can't be that the prime minister is not involved."

Israeli police on Wednesday questioned David Shimron, Netanyahu's cousin and personal attorney, following revelations that he represented the German firm involved in the $1.5 billion deal, raising the prospect of a conflict of interest.

Shimron told reporters after leaving the investigators' offices near Tel Aviv that he "must respect the investigation and the investigators," and that he therefore could not comment. Netanyahu, who is not a suspect in the case, has denied any wrongdoing.

Police suspect Shimron was hired by the German firm because of his ties to Netanyahu. Police reportedly barred Shimron from communicating with Netanyahu, and Israeli representatives of German shipbuilder ThyssenKrupp from discussing the case with their parent company.

Israeli police have declined to go into detail about the investigation.

Israel has ordered six submarines from Germany in the past two decades, with the final one scheduled for delivery in 2018. Israel recently decided to purchase three new vessels to replace its older submarines.

Yaalon recalled heated conversations with Netanyahu over buying the extra submarines that he said ended in "unpleasant tones." Yaalon said there was no urgent need for the vessels.

Police have questioned Netanyahu over separate corruption allegations regarding questionable ties to top media, business and Hollywood executives. Netanyahu has dismissed those accusations as "baseless."