A "disorderly" default in Greece could cause more than €1trn (£833bn) damage to the eurozone, a confidential report has warned.
A document published by the Institute of International Finance (IIF), obtained by Reuters, suggested a default would leave Italy and Spain needing outside help to stop risks spreading.
"There are some very important and damaging ramifications that would result from a disorderly default on Greek government debt," the IIF said.
"It is difficult to add all these contingent liabilities up with any degree of precision, although it is hard to see how they would not exceed 1 trillion euros."
The IIF has called on bondholders to sign up by a Thursday deadline for a bond swap deal aimed at saving Greece more than €100bn and putting the country on a more stable footing.
If it fails to win support, the ECB would likely suffer substantial losses, the document said, estimating the central bank's exposure to Greece was €177bn euros, more than 200% of its capital base.
Both Ireland and Portugal would need more outside help to insulate them from Greece, which could cost €380bn euros over five years, the IIF estimated.
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