Jerusalem (AFP) - Israeli Prime Minister Benjamin Netanyahu has lashed out at police over claims detectives probing graft allegations against him were targeted by private investigators as the probe reportedly nears completion.

Pressure has built on Netanyahu with police investigating him reportedly set to hand over their recommendations to the attorney general next week in the long-running probe.

Israeli media have reported that police are expected to recommend that the long-serving prime minister be indicted for bribery, fraud and breach of public trust.

Israeli authorities have refused to comment publicly on the reports. The attorney general is expected to take weeks or months to decide how to proceed after receiving the recommendations.

On Monday night, Police Commissioner Roni Alsheich said in an interview with Israel's Channel 2 television that detectives probing Netanyahu had been targeted by private investigators to dig up dirt on them.

Netanyahu posted a response on Facebook late Wednesday in which he lashed out at the police commissioner, calling suggestions that he sent private investigators on such a mission "ridiculous."

"It is shocking to discover that the commissioner has repeated the mistaken and ridiculous suggestion that Prime Minister Netanyahu sent private investigators after the police who are investigating him," the post said.

He also referred to claims that sexual harassment allegations against the head of the unit investigating Netanyahu were an attempt to smear him because of the graft probe.

"Any honest person would ask himself how people who say such delusional things about the prime minister can objectively investigate him and honestly give unbiased recommendations," the post said.

"A large shadow was cast tonight over the police investigations and their recommendations related to Prime Minister Netanyahu."

The investigation has raised the possibility that Netanyahu, prime minister for a total of nearly 12 years, will eventually be forced to resign.

Police are investigating Netanyahu over suspicions that he received expensive gifts from wealthy supporters as well as over allegations that he sought a secret deal for favourable coverage with a newspaper publisher.

The 68-year-old premier has repeatedly denied any wrongdoing and says he is being targeted by political opponents.