The republican presidential candidate Nicholas Sarkozy, who was France's president from 2007 to 2012 before losing to current president, Socialist Francois Hollande, was attacked by several of his former ministers and party allies. They questioned why he would be any different than in his first term and noted he faces multiple judicial investigations into alleged corruption, fraud and campaign funding irregularities.

"Ten years ago, in 2007, I believed in Nicolas Sarkozy's plan to break with the past, but it never happened," former conservative party leader Jean-Francois Cope said. "If I had been put under formal investigation, I wouldn't have run (in this election)," he said.

Sarkozy, who denies any wrongdoing, retorted that such accusations "do not honor those who make them." He appeared quite tense at times while Juppe was subdued, apparently wanting to avoid any move that could hurt his lead in the race.

Former Prime Minister Alain Juppe was seen as the winner of the first debate on Thursday among candidates for the center-right's nomination in France's 2017 presidential election, a poll published immediately afterward showed.

Juppe, already the front-runner on a centrist platform of "happy identity" which he said in the televised debate meant giving voters hope, was seen as most convincing by 32 percent of those who said they would vote in the end-November primaries.

The poll was conducted as an online survey of 885 voters by polling firm Elabe commissioned by news network BFM TV.

Sarkozy, a former president running on a law-and-order agenda meant, he said, "to ensure France once more becomes the great nation it is," convinced 27 percent of voters in the two-hour debate. There were more differences on issues of security and immigration, with contenders quarrelling over whether those on intelligence services' watch lists should be systematically detained.

All were harsh in their criticism of Hollande, the most unpopular French president on record and a likely opponent in the April 2017 presidential election.

Two more televised debates will follow before the first round of the primaries, scheduled for Nov. 20.