Israeli Foreign Minister Tzipi Livni's advantage as front-runner in the leadership race for her centrist Kadima party has narrowed, according to a public opinion poll published on Friday.

Kadima, currently headed by Ehud Olmert, will hold a September primary that could lead to the embattled prime minister's replacement. It is unclear whether Olmert, facing several corruption investigations, will choose to stand.

Even if Olmert were to stand, Livni has been seen as most likely to win, but the poll in the Yediot Aharonot daily showed that former defence minister and current transport minister Shaul Mofaz is narrowing that gap.

Asked to choose among five theoretical candidates including Olmert, 35 percent said they backed Livni and 26 percent opted for Mofaz. That compared with 37 percent for Livni in a poll on July 11 and 22 percent for Mofaz.

Friday's poll predicted an even closer race if only the two were running, with Livni at 47 percent and Mofaz at 45 percent.

That would leave the race wide open, given that the margin of error in the survey was 4.5 percentage points.

Kadima is holding the primary only because the Labour party, its key partner in the coalition government, said it would pull out if Olmert was not replaced. Without Labour Kadima would not have a majority in parliament.

Olmert has been dogged by six corruption investigations since he took power in 2006 and faces mounting calls to step down.

Public Security Minister Avi Dichter and Interior Minister Meir Sheetrit are also considered potential candidates for Kadima's leadership. However the poll showed that between them they had the support of just 15 percent of respondents.