S&P: Eurozone debt restructuring not inevitable - The Best from Greece

"It's certainly not inevitable," Kraemer said when asked if the conditions of the new European Stability Mechanism would meant Portugal, Greece and Ireland would be forced to restructure their public debt.

"With the exception of Greece they are still in investment grade meaning that we continue to believe a restructuring (is) quite unlikely in those cases. However, the risks have marginally increased because of this conditionality," he added.

European leaders agreed a new package of anti-crisis measures at a two-day summit in March, sealing a deal on funding the ESM -- a new, permanent safety net that will become operational in mid-2013.

Countries that resort to the mechanism may be forced to restructure private debt before getting support.