Israeli Interim Prime Minister Ehud Olmert has formed a coalition government, a month after national elections. A precarious alliance with a religious party could create future political instability.

After three weeks of negotiations, Ehud Olmert completed the formation of a new government by adding the ultra-Orthodox Shas Party to the coalition. The new government will control 67 seats in the 120-member Knesset, Israel's parliament.

But the partnership with Shas puts an obstacle in the way of Mr. Olmert's top priority - his plan for drawing Israel's final borders by 2010. Shas, which has a hawkish constituency, refused to sign a key part of the coalition agreement, which calls for dismantling settlements and withdrawing from large parts of the West Bank.

Shas leader Eli Yishai told Israel Radio that Shas would consider trading territory as part of a peace agreement with the Palestinians, but he said the party opposes the unilateral pullouts planned by Mr. Olmert.

He said abandoning territory without a peace agreement is a reward for Palestinian terrorism and would encourage more violence.

Mr. Olmert is promoting unilateral steps because he believes a peace agreement is impossible now that the Islamic militant group Hamas controls the Palestinian Authority. Hamas seeks Israel's destruction.

Shas is not an ideal partner for the center-left coalition led Mr. Olmert's Kadima Party and the dovish Labor Party. But without Shas, Mr. Olmert did not have enough parliament seats for a majority government.

The alliance underscores the precarious nature of Israeli politics. Governments rarely serve out their four-year terms. Analysts expect Shas to quit the coalition when the time comes to remove some 70,000 Jewish settlers from their West Bank homes in about two years. So, the new Olmert government could suffer the same fate as its predecessors, and collapse.