EU sources recently said that eurozone governments may have to offer up to 145 billion euros to Athens under a second emergency loan program for Greece. The extra funds are primarily required for helping recapitalise the Greek banking sector once a deal is struck to write down the value of bonds owned by private-sector creditors, the sources said.

"It's mostly because of recapitalisation needs of Greek banks due to PSI," one euro zone official said, referring to bondholder losses termed private sector involvement.

"The agreement of the leaders in October was for 100 billion euros in financing for Greece and 30 billion euros as a sweetener for the debt swap for the private sector. Now it could be 115 billion plus 30 billion," the second source said.

The increase in size of the contribution of euro zone taxpayers to the second Greek financing package was not a done deal yet, the officials said because there was resistance to the idea from some euro zone countries.

"It is difficult to tell if this will be accepted," a third euro zone official said of the higher public financing.

The debts of Greece must be cut from around 160 percent of GDP now to 120 percent of GDP by 2020 in order to be sustainable, according to the International Monetary Fund.