Polls have opened across Israel in the ruling Likud Party's primary vote, in which a veteran lawmaker will try to unseat Benjamin Netanyahu - the prime minister's first serious internal challenge in more than a decade in power.
Former Minister of Education Gideon Saar, who officially launched his bid to unseat Netanyahu earlier this month, argues that he will be better placed to form a government in national elections in March after Netanyahu failed to do so twice in two repeat elections this year.
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Netanyahu is expected to defeat Saar in Thursday's polls, such a win could strengthen his hand going into the next national vote.
Netanyahu remains popular among Likud members despite the shadow of corruption indictments hanging over him. The Likud, which has only had four leaders since its inception in the 1970s, has stood firmly behind the long-serving leader.
Although Saar is still a decided underdog to the embattled prime minister, he seemed to be gaining traction in the run-up to the Thursday vote among the party faithful and could benefit from stormy weather that may keep turnout low.
If he wins, Saar would become Likud's candidate for prime minister in the March polls.
"We are imbued with the spirit of victory," legislator Yoav Kisch, Saar's campaign manager, told Israeli Army Radio. "This candidacy is good for the party and I believe can also bring the change and the hope for a revolution in the Likud."
Corruption cases
Netanyahu faces charges of bribery, fraud and breach of trust in three corruption cases in which he is accused of trading legislative or regulatory favours in exchange for lavish gifts or favourable media coverage.
He denies wrongdoing and has waged a campaign against media and law enforcement officials he claims are bent on removing him from office.
Outwardly, Likud members have strongly supported their leader and joined in denouncing the alleged "coup" of the liberal elites against him.
But Saar's burgeoning insurrection has begun to reveal some cracks.
About 500 party activists attended the launch of the veteran politician's campaign to unseat Netanyahu, held in the Tel Aviv suburb of Or Yehuda. Saar's campaign has been buoyed by support from six Likud legislators, including the powerful chairman of the party's executive body.
Voting ends at 11pm (21:00 GMT) and results are expected early Friday.
Israel hits Gaza
On the eve of the vote, the Israeli military said it carried out air strikes against Gaza on Wednesday night, in what it called a response to a rocket fired from the Palestinian enclave.
Warning sirens cut short a rally by Netanyahu as he campaigned ahead of the vote, public television reported.
"Planes and helicopters hit several Hamas terrorist targets in the Gaza Strip. Military posts were among the targets," the Israeli army said in a statement.
The army had earlier said "a projectile was fired from the Gaza Strip towards Israeli territory and was intercepted by the Iron Dome defence system".
Last week, Israeli warplanes attacked Gaza early after Palestinian fighters in the enclave fired a rocket towards southern Israel. Successive air attacks targeted sites in Gaza City that the Israeli military said were "a Hamas weapons manufacturing site".
No Palestinian group claimed responsibility for the rocket fire.
Hamas has controlled Gaza since 2007 and Israel holds the movement responsible for all rocket fire coming from the territory, although it has targeted other armed groups there.
Since 2008, Israel has waged three wars against Hamas and its armed allies in Gaza, where two million Palestinians live amid violence, poverty and a 10-year Israeli blockade.