Voting has ended in the Israeli Labor Party's leadership election, a contest which could determine the fate of Prime Minister Ehud Olmert's government.

Early exit polls indicate that the defense minister, Amir Peretz, has lost his bid to remain head of the party.

But neither former Prime Minister Ehud Barak nor the former head of Shin Bet, Ami Ayalon, appear to have won the 40% of votes needed to avoid a run-off.

Preliminary results are expected to be announced at 2330 (2030 GMT).

The leadership contest has been described as the most significant moment for Labor in the last 15 years.

Both Mr Barak and Mr Ayalon have threatened to pull the party out of the ruling coalition unless Mr Olmert steps down from office.

This follows damning criticism of his leadership in an official report on the handling of the Lebanon war last year.

Close call

The BBC's Mike Sergeant in Jerusalem says the race is much too close to call, with exit polls for two Israeli television channels predicting two different results.

A poll for Channel Two said Mr Ayalon was on track to win 39% of the vote, compared to 33% for Mr Barak and 19% for Mr Peretz.

Israel TV said its poll gave Mr Barak 38%, Mr Ayalon 36%, and Mr Peretz 17%.

Both polls, however, predicted the two men would fail to reach the 40% threshold required to avoid a run-off election on 12 June.

Labor officials said at least 58% of the 103,498 party members voted in the election.

Final results for the election are expected on Tuesday morning.

Fresh faces

Mr Barak, who served as prime minister from 1999 to 2001, has been the biggest name in the race.

During his two turbulent years in office, Israeli troops withdrew from Lebanon, peace talks ended in failure and the Palestinian intifada, or uprising, began.

Mr Barak still has many enemies in Israel and within his own party.

They accuse him of arrogance, and a stubborn refusal to delegate or listen to advice when in office. The former prime minister says he is a changed man.

During the campaign, Mr Barak has shunned the media, instead spending all his time talking direct to party members.

But, according to BBC correspondent, that direct contact with party members has not given him a clear advantage over Israel's former internal security chief, Mr Ayalon.

A relative political novice, Mr Ayalon has been in parliament for just one year.

But that gives him fresh appeal, BBC correspondent says, and he has vital experience in the area that matters the most to Israelis - security.

Photo caption

Ehud Barak and Ami Ayalon