Israel's PM Benjamin Netanyahu has warned that a proposed unity government aimed at replacing him would be a danger to the country's security.
He urged fellow right-wingers not to back a deal after ultra-nationalist Naftali Bennett said he would form a coalition with a centrist party.
Mr Netanyahu's opponents have until Wednesday to form a government.
If they are successful, it would bring to an end the rule of the country's longest-serving prime minister.
Mr Netanyahu, who faces serious corruption charges and could go to jail, fell short of a decisive majority at a general election in March. It was the country's fourth inconclusive vote in two years - and again he failed to secure coalition allies.
But his opponents may only be able to form a minority government, propped up by Arab members of parliament.
Tensions remain following the recent Gaza conflict, which also triggered inter-communal clashes in Israeli cities between Jews and Arabs.
Some Arab politicians could be reluctant to join a government led by Mr Bennett, who supports expanding Jewish settlements in the Palestinian West Bank.
'Fraud of the century'
"Don't form a left-wing government - such a government is a danger to Israel's security and future," 71-year-old Mr Netanyahu, who has dominated Israeli politics for a generation, said on Sunday.
Naming left-wing leaders who, he hinted, could weaken Israel's security cabinet, he asked: ""What impact will that have on Israel's deterrent capability? How will we look to our enemies? What will they say in Iran and Gaza?"
Mr Netanyahu accused Mr Bennett of "misleading the public" and of carrying out "the fraud of the century" - a reference to the Yamina party leader's previous public promises not to join forces with Yair Lapid, the centrist opposition leader.
Mr Bennett, 49, earlier announced in a televised address that his party would join talks to form a unity government.
"Mr Netanyahu is no longer trying to form a right-wing government because he knows full well that there isn't one. He is seeking to take the whole national camp, and the whole country, with him on his personal last stand," Mr Bennett said.
"I will do everything to form a national unity government with my friend Yair Lapid."
Before the announcement, Israeli media reported that under the proposed terms of the deal, Mr Bennett would replace Mr Netanyahu as prime minister and later give way to Mr Lapid, 57, in a rotation agreement. The arrangement has not been officially confirmed.
The proposed coalition would bring together factions from the right, the left and the centre of Israeli politics. While the parties have little in common politically, they are united in their desire to see Mr Netanyahu's time in office come to an end.
Mr Lapid, a former finance minister, was given until 2 June to form a new coalition government after Mr Netanyahu failed to do so. His Yesh Atid party came second to Mr Netanyahu's right-wing Likud at the last election.
Source: BBC
BDST: 1348 HRS, MAY 31, 2021
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