Tel Aviv - Israeli Foreign Minister Tzipi Livni won a narrow victory in the leadership primary of Israel's Kadima party, defeating her main rival, Transport Minister Shaul Mofaz, by only a handful of votes, Israel Radio reported early Thursday morning.

Livni won with 43.1 per cent, compared to 42 per cent for Mofaz, a difference of only 431 votes.

But Mofaz's headquarters said the final difference between the candidates was only 1 vote, and it is likely the disappointed candidate will mount a legal challenge against the result, citing voting irregularities in several polling stations, and the fact that voting was extended for 30 minutes on Wednesday.

The other two candidates in the race, Interior Minister Meir Sheetrit and Public Security Minister Avi Dichter, won 8.5 per cent of the vote and 6 per cent respectively.

The final result was much closer than predicted by television exit polls when voting closed Wednesday night. All three Israeli television channels had predicted Livni winning with 47 to 49 per cent of the vote, to around 37 for Mofaz.

The Kadima primary is considered one of the most crucial in Israel's history, with party members determining who might well become the country's next prime minister.

The victorious candidate will replace Ehud Olmert, who announced in July that he would quit the premiership, because of ongoing investigations against him for alleged corruption.

The primary could also be decisive for the peace process with the Palestinians, with Livni, Israel's chief negotiator and - although a centrist - a staunch advocate of a two-state solution to the Middle East conflict, likely to continue negotiations according to their current format.

Mofaz, by contrast, is a comparative hawk in the centrist party, who has openly and repeatedly said he opposes dividing Jerusalem and wants to postpone negotiations on a final peace deal.

Livni, if she succeeds in forming a government, will become the second female prime minister in Israel's history. (dpa)