US President George W Bush has been caught on microphone using an expletive as he discussed Hezbollah's rocket attacks on Israel.
Mr Bush was heard telling UK Prime Minister Tony Blair privately that Syria should press the Lebanese militants to "stop doing this shit".
The remarks were picked up by closed-circuit TV at the G8 summit which both leaders are attending.
Mr Bush also said US Secretary of State Condoleezza Rice would go to the area.
Mr Blair was heard saying Ms Rice had to succeed in the mission.
He also appeared to discuss a proposal to send international forces to Lebanon to prevent the attacks on Israel.
The remarks came as the two leaders were sitting down to lunch at the summit in the Russian city of St Petersburg.
"The irony is, what they really need to do is to get Syria to get Hezbollah to stop doing this shit, and it's over," Mr Bush was heard to say.
Soon after Mr Blair noticed that the microphone was open and switched it off, reports say.
The summit has been discussing what to do about the crisis, triggered by the capture of two Israeli soldiers by Hezbollah last week.