A run-off will be held after no candidate won sufficient votes in Israel's Labour party leadership elections.

The votes are still being counted but according to a party official no candidate reached the required 40 per cent mark,

The two leading candidates will compete in another round of voting by party members on September 21.

The run-off is to be a fight between the onetime Defence Minister Amir Peretz and former television presenter Shelly Yachimovich. Former cabinet minister Isaac Herzog is believed to have been in third place.

In Israel's early years Labour was a dominant political force. But it has been of declining influence in Israeli politics for several years and last January lost key members when Defence Minister Barak formed a new leftist "Independence" party.

The winner of the leadership election will have more than a year to establish themselves as an opposition figure; Prime Minister Benjamin Netanyahu does not have to face the polls until 2013.