Germany's finance minister says private holders of Greek government bonds must accept bigger losses to achieve "a durable and sustainable solution" for Europe's debt crisis.

Wolfgang Schaeuble told German public broadcaster ARD on Sunday that an agreement struck in July when banks and other investors agreed to renounce on 20 percent of their Greek debt must be renegotiated.

He says the private sector's contribution to a reduction of Greece's debt burden "will probably have to be higher."

The Institute of International Finance, a global bank lobbying group, says its managing director Charles Dallara is in talks with officials from the 17-nation eurozone about the July agreement. Spokesman Frank Vogl declined to elaborate, but the group's leadership has so far rejected accepting bigger losses.