With contagion spreading, a majority of twenty prominent economists polled by Reuters predicted that the euro zone was unlikely to survive the crisis in its current form, with some envisaging a "core" group that would exclude Greece.

Investors were also unnerved by reports that Belgium is leaning on France to pay more into emergency support for failed lender Dexia under a 90-billion-euro ($120-billion) rescue deal that had appeared done and dusted.

A special report by Fitch Ratings suggested France had limited room left to absorb shocks to its finances, such as a new downturn in growth or support for banks, without endangering its triple-A credit status.