Israel's president tasked Prime Minister Benjamin Netanyahu on Wednesday with assembling a new government after power-sharing talks with his strongest rival, Benny Gantz, failed following an inconclusive election.

But right-wing Likud party chief Netanyahu, facing a looming indictment on corruption allegations he denies, still has no clear path to a fifth term after emerging from the Sept. 17 ballot, the second this year, short of a parliamentary majority.

Accepting the mandate from President Reuven Rivlin at a televised ceremony, a politically weakened Netanyahu said his chances of success were only marginally higher than those of Gantz, a former general who heads the Blue and White party.

In his remarks, Netanyahu seemed to envision a scenario in which he and Gantz would be able to take another stab at power-sharing once it became clear there was no way out of the current deadlock, save for a third election that few in Israel wanted.

"If I don't succeed, I will return the mandate to you and with the help of God and Israel's citizens and yourself, Mr President, we will establish a broad national unity government down the line," he said.

Netanyahu, 69 and Israel's longest-serving leader, will have 28 days to form a coalition and can ask Rivlin for a two-week extension if necessary. Netanyahu's failure to clinch victory in a ballot in April led to last week's election.

Rivlin, in his remarks, pointedly noted that he is under no obligation to grant his prime minister-designate that two-week extension to establish a governing coalition.

Nor did he commit to turning to Gantz if Netanyahu failed to break the current deadlock. Under law, Rivlin can assign the coalition-building task to any member of parliament he deems likely to succeed, or he can ask the legislature to pick someone.

With final results announced on Wednesday, Likud has the pledged support of 55 legislators in the 120-member parliament, against 54 for Blue and White. The two parties failed to reach a coalition deal in talks launched on Tuesday.

Former Defence Minister Avigdor Lieberman, a possible kingmaker, has been keeping his far-right Yisrael Beitenu party on the fence since the Sept. 17 ballot, citing differences with Likud's ultra-Orthodox religious partners and Blue and White's left-wing allies.

"It became clear that neither Netanyahu nor Gantz had the 61 seats necessary to form a government," Rivlin said at the ceremony.

"Netanyahu's ability to assemble an administration is higher at the moment," the president said, noting that 10 Arab legislators in Gantz's support bloc of 54, who recommended he nominate the ex-general, did not commit to joining a government.

Rivlin had until next Wednesday to announce his choice, but the Likud-Blue and White unity talks showed no sign of progress.

A deal in which Netanyahu and Gantz would take turns as prime minister was widely mooted.

But in his campaign, Gantz pledged not serve in a government with Netanyahu, citing the Israeli leader's legal troubles. And Gantz's deputies in Blue and White also voiced their strong opposition while the unity talks were under way.

Next month, Israel's attorney-general will hold a pre-trial hearing on his announced intention to indict the Israeli leader on fraud and bribery charges in three corruption cases. Netanyahu, who says he is a victim of a political witch-hunt, can argue at the session against being charged.

As prime minister, Netanyahu would be under no legal obligation to resign if formal charges were filed. But any other cabinet post might not offer him that protection.