A former Israeli minister on Sunday started serving a 15-month jail sentence for fraud and breach of trust, judicial sources said.

Stas Misezhnikov, who was tourism minister from 2009 to 2013, was sentenced to prison in October for handing one million shekels ($280,000) in financial support to a student festival while securing a job at the event for a woman with whom he had an intimate relationship.

Misezhnikov starts serving time as public pressure increases to demand legal action against "corrupt" officials and Prime Minister Benjamin Netanyahu himself faces two separate graft probes.

Misezhnikov is a member of Defence Minister Avigdor Lieberman's ultra-nationalist Yisrael Beitenu party.

In August, Yisrael Beitenu secretary general Faina Kirshenbaum, who was deputy interior minister from 2013 to 2015, was charged with corruption, breach of trust, fraud and money laundering.

On Saturday, thousands of Israelis protested for a third week running in Tel Aviv to demand legal action against "corrupt" people in the government and their resignation.

The demonstration came a day after Netanyahu was questioned for the seventh time since January 2 in a corruption probe.

In one investigation, the prime minister is suspected of illegally receiving gifts from wealthy personalities including Australian billionaire James Packer and Hollywood producer Arnon Milchan.

In a second case, police suspect Netanyahu sought a secret pact for favourable coverage with the publisher of the top-selling Yediot Aharonot newspaper.

The alleged scheme, not believed to have been finalised, would have seen him receive favourable coverage in return for helping curb Yediot's competitor, the pro-Netanyahu freesheet Israel Hayom.

The 68-year-old premier has consistently denied any wrongdoing, and says he is the target of a smear campaign by political opponents.