The interest rate which Greece has to offer to borrow money for ten years rose to 7.631% on international bond markets this morning, above a level which Athens has already called untenable.
The rate, or yield on the bonds, eased slightly to stand at just under 7.5% this evening compared with 7.366% on Friday.
The latest rate means that Greece has to pay 4.4 points more than euro zone benchmark country Germany to borrow for ten years.
The high yield on Greek bonds is also affecting yields on debt issued by some other euro zone countries considered to have heavy debt and public deficits.
The yield on Portuguese 10-year debt rose to 4.629% today from 4.462% on Friday, and on debt issued by Ireland to 4.5951% from 4.555%.
At the end of last week, Greece said that it was doing all the preparatory work needed in the event that it asks the European Union and International Monetary Fund to activate a debt-rescue package.
The package, to make available up to €30 billion from the EU and half as much again from the IMF in the first year, has been agreed in principle.
But a visit to Athens by experts from the EU, the European Central Bank and the IMF to clarify the terms and conditions, and crucially the interest rate which Greece would have to pay, has been delayed until Wednesday because of disruption to air traffic caused by volcanic ash from Iceland.
This has left financial markets in considerable uncertainty over the outlook for management of the Greek debt crisis which has already weakened the euro, caused deep disagreements within the European Union, and undermined the prestige and outlook for the euro zone.
Greece is due to try to raise €1.5 billion with the issue of short-term three-month treasury bills tomorrow. The country must borrow about €11 billion by the end of May just to redeem old debt falling due and avoid partial default.
