Shares in Greek banks are plunging on the Athens Stock Exchange amid expectations they will have to accept higher than agreed losses on the country's government bonds as part of a new eurozone debt deal.

Greek banks hold billions in the country's government debt.

Bank stocks were down on average by about 15 percent midday Monday, pulling the exchange's general index down 4.8 percent to 744.56. Other European stock indexes were buoyed by the prospect of a debt agreement.

Leaders of the 17-nation eurozone, fearing the crisis could spread from debt-shackled countries like Greece to larger economies, failed to clinch a comprehensive debt deal at a weekend summit. They expect to finalize an agreement by Wednesday.