Banks are pushing back against European leaders on the size of losses they are ready to accept on Greek bonds as officials struggle to rescue the debt-laden country while avoiding a default.

There are limits "to what could be considered as voluntary to the investor base and to broader market participants," Charles Dallara, managing director of the Institute of International Finance, an industry group that's participating in the talks on Greek debt, said in an e-mailed statement yesterday. "Any approach that is not based on cooperative discussions and involves unilateral actions would be tantamount to default."

The discussions are part of an attempt to solve the two-year-old sovereign-debt crisis that has pushed Greece toward default and roiled global markets. European Union leaders, who hold a second summit in four days tomorrow, are seeking an agreement on bolstering the region's rescue fund, recapitalizing banks and providing debt relief to Greece to avoid contagion spreading to Italy and Spain.