Designated Prime Minister Benjamin Netanyahu was still one partner short of a coalition to secure a parliamentary majority on Wednesday after an ultra-Orthodox Jewish party signed up, with the deadline for forming a government looming.
The deal with United Torah Judaism (UTJ), announced late on Tuesday, promised Netanyahu control of 53 of the Knesset's 120 seats with his conservative Likud party. That left Shas, an ultra-Orthodox party with 11 seats, as Likud's last likely ally.
After coming ahead in a Nov. 1 election, Netanyahu was given 28 days to present a coalition. Commentators predicted he would do so in short order, given the strong showing of religious-nationalist parties. But negotiations have proven protracted.
The inclusion of far-rightists in the incoming government has stirred fear at home and abroad for the future of Israel's long-moribund talks with the Palestinians and fraught ties between its majority Jews and 21% Arabs citizens.
Netanyahu has said he will serve all Israelis but has not indicated any plan for reviving talks with Palestinians.
UTJ said in a statement on the Likud deal, which it agreed even though some details were pending, that talks needed to be extended beyond Sunday's deadline for a coalition agreement.
President Isaac Herzog can extend the mandate by 14 days.
Among issues dogging the coalition talks is a tax-fraud conviction of Shas leader Arieh Deri, a candidate for finance minister. Shas has submitted legislation that would enable Deri - who was spared jail under a plea deal - to serve in cabinet.
Netanyahu has yet to request an extension for coalition talks. But the centrist opposition has accused him of planning to use any extra time he might get to push the Deri-linked bill through parliament before his government is in office.
Outgoing Justice Minister Gideon Saar said on Twitter that any request for extra time would be a "ruse (to enable) the passing of personalized and problematic laws, in accordance with the demands of (coalition) partners, before the government is set up."
United Arab List (UAL), a party that draws support from Israel's Arab citizens and which was part of the outgoing coalition, signaled it might be willing to join Netanyahu.
"I'm not ruling this out," UAL leader Mansour Abbas told 103 FM radio, saying he awaited word on the new government's policies.