President Sarkozy appears to have revealed his true feelings for Israel's Prime Minister - calling him a liar in private conversation picked up by microphones they thought were turned off.

The French leader was apparently overheard talking to President Obama about Benjamin Netanyahu at last week's G20 summit.

He told him: "I cannot stand him, he's a liar". President Obama was heard to reply: "You may be sick of him, but me, I have to deal with him every day."

The remarks were made in a private room last week during the Cannes G20 summit when the pair were discussing France's decision to back the Palestinian UNESCO bid, against US wishes.

What neither man realised was that their microphones - attached ahead of a press conference – were already switched on. Journalists waiting nearby heard everything.

The three-minute exchange was first reported on a French blog and confirmed later by a Reuters reporter who also heard it. Reporters had agreed not to expose it at the time as it was too sensitive.