French President Nicolas Sarkozy, who has labored to improve French relations with Israel, said he "can't stand" Israeli Prime Minister Benjamin Netanyahu and called him a liar in a chat with President Barack Obama.

The conversation between Sarkozy and Obama was overheard by reporters last week at the Group of 20 summit in southern France, via headsets that were to be used for simultaneous translation of an upcoming news conference.

In the remarks Thursday in Cannes, Sarkozy said: "Netanyahu, I can't stand him. He's a liar."

According to the French interpreter, Obama responded, "You are sick of him, but I have to work with him every day."

The journalists heard only fragments of the leaders' conversation.

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Obama, whose remarks were heard via a French translation, was not heard objecting to Sarkozy's characterization of Netanyahu. Through the interpreter, Obama was heard asking Sarkozy to help persuade the Palestinians to stop their efforts to gain U.N. recognition of a Palestinian state.

Several French-speaking journalists, including one from The Associated Press, overheard the comments but did not initially report them because Sarkozy's office had asked the journalists not to turn on the headsets until the press conference began, and the comments were deemed private under French media traditions.

A French website that analyzes media coverage of current affairs, Arret sur images, reported the fragments Tuesday.

Sarkozy's office would not comment Tuesday on the remarks, or on France's relations with Israel. The White House and Netanyahu's spokesman also said they had no comment.

Since becoming president in 2007, Sarkozy has strengthened French ties with Israel while also seeking to use France's traditional good relations with Arab allies to encourage peace talks.

His latest comments reflect his increasing frustration with Netanyahu, and may complicate French efforts toward Mideast peace.

France's government has not said so officially but appears to see Netanyahu as partially responsible for the deadlock in peace talks. France has repeatedly urged Netanyahu to stop building Jewish settlements in the West Bank and come to the negotiating table, to little avail.

"I think all this must not make us lose sight of the basics -- which is to say there's not a minute to lose to continue to work on the Israeli-Palestinian issue," French Foreign Ministry spokesman Bernard Valero told reporters Tuesday.

"In our relationship with Israel, as with our relationship with the Palestinians, what we want is to continue to work so that things move ahead -- because they're not moving ahead," Valero said.

The overheard remarks by Sarkozy and Obama were prominently covered in Israel, where Sarkozy -- whose maternal grandfather was Jewish -- is widely perceived as a friend, in striking contrast to some of his predecessors, including Jacques Chirac, whom Sarkozy replaced in 2007.

Israel has had a fraught up-and-down relationship with France. The country was an early supporter of the Jewish state, selling it arms and planes and helping it develop a nuclear reactor. But the relationship soured under Charles de Gaulle, perceived as having abandoned Israel before the 1967 war.

"There has been improvement of the relationship since Sarkozy took over," Avi Pazner, who was Israel's ambassador to France in the 1990s, said Tuesday. "He has shown himself as a friend of the state of Israel."

In comments at the G-20 last week, Sarkozy said that if Israel's existence is threatened, "France will not stand by with arms crossed."

Netanyahu, meanwhile, is a controversial figure even at home. He is widely seen as divisive, and is regularly pilloried by the center-left opposition for preferring settlement construction in the West Bank to peace talks with a relatively moderate Palestinian leadership.

"Obama is wrong," wrote one reader on the Israeli newspaper Haaretz's web site. "We're the ones that have to deal with him every day."

The often blunt Sarkozy has shown little patience with Israeli hard-liners, and two years ago urged Netanyahu to fire his outspoken foreign minister, Avigdor Lieberman. In a private meeting, Sarkozy told Netanyahu that "you must get rid of that man," according to two officials.

This September, the French leader tried to head off the Palestinians' request for membership in the United Nations with a last-minute effort to revive peace talks.

But France then surprised Washington and other observers by voting last week in favor of membership for Palestine in UNESCO, the U.N. cultural and educational agency.

Remarks overheard by journalists have embarrassed world leaders in the past. At a Group of Eight summit in 2006, an open microphone caught then-British Prime Minister Tony Blair appearing subservient to President George W. Bush, who greeted him by shouting, "Yo, Blair!"