Israeli Foreign Minister Tzipi Livni said Friday she "regrets" her main party rival Shaul Mofaz's decision to leave politics.

Chairing the first meeting of Israel's ruling party a day after she won the Kadima leadership, Livni said she had made it clear to Mofaz in their private conversations that she had planned to work with him.

Mofaz, who was defeated by Livni by just 1.1 per cent of Wednesday's vote, made a surprise announcement late Thursday that he would resign from the government and Knesset (parliament.)

He did not attend Friday's first Kadima meeting headed by Livni at the centrist party's headquarters in Petah Tiqwa, north-east of Tel Aviv.

Livni, welcomed with flowers at the headquarters, expressed hope other Israeli factions would "show responsibility" in the upcoming coalition negotiations.

If they did not, she would not hesitate to enter into early elections and win, she vowed, Israel Radio reported.

Livni Thursday was announced winner of Kadima primary, after official results showed her winning 43.1 per cent of the vote, against 42 per cent for Mofaz, a difference of 431 votes.

Israeli Prime Minister Ehud Olmert plans to resign either early next week or by October 2 amid corruption allegations, allowing her to try and form a new coalition.