ATHENS - The euro zone must take immediate action to overcome scepticism over its ability to respond to the spreading debt crisis, Greek Prime Minister George Papandreou said on Friday.

"Recent developments mainly reflect an increasing scepticism about the systemic capacity of the euro area to respond to the ongoing crisis," Papandreou wrote in a letter to European Commission President Jose Manuel Barroso.

"The decisions having been taken by the leaders (at an emergency euro zone summit last month), the appropriate European institutions as well as member-states should proceed now to action and, in particular the national parliaments, where that is necessary," he wrote.

Papandreou was referring to implementation of the summit's decision to boost the powers of the euro zone's EFSF rescue fund and grant Greece a new bailout.

(Reporting by Ingrid Melander; editing by Barry Moody)