French President Nicolas Sarkozy is to telephone German Chancellor Angela Merkel around midday on Tuesday after Greece announced it would hold a referendum on a debt rescue package, the Elysee palace said. Greek Prime Minister George Papandreou\'s surprise announcement on Monday of a referendum on last week\'s EU debt deal in the hope of silencing widespread domestic opposition to austerity measures sent stock markets tumbling on Tuesday. Analysts said it could be seen as a vote on membership of the eurozone.