ATHENS--National Bank of Greece SA, Greece's largest lender, swung to a robust fourth-quarter profit of more than half a billion euros thanks to a series of tax benefits carried over from earlier years that helped offset continuing large provisions for bad loans.

The bank said it earned 547 million euros ($754 million) in the three months to the end of December last year, compared with an EUR81 million loss in the third quarter, reflecting EUR531 million in income from deferred tax assets and exceptional items.

Excluding those accounting gains, the bank had a net profit of EUR16 million in the final quarter of 2013, compared with EUR8 million in the third quarter. Provisions remained high at EUR388 million in the fourth quarter, little changed from the July-September period.

Due to a series of mergers and material changes to Greece's banking system, NBG's latest earnings aren't directly comparable with year-earlier data.

After a deep, six-year recession, the pricking of the Greek property bubble, withdrawals by depositors and a EUR200 billion sovereign-debt restructuring, Greece's banks are struggling. Last year, they were recapitalized with the help of a European Union loan, but together the banks still hold some EUR70 billion in bad loans, a sum equal to a third of Greece's annual gross domestic product.

Earlier this month, Greece's central bank said the country's four big lenders-NBG, followed by Piraeus Bank SA, Alpha Bank AE and Eurobank Ergasias-would need to raise another EUR5.8 billion to shore up their fragile balance sheets and cope with that mountain of bad loans The Bank of Greece said the four banks would need to present plans by mid-April detailing how they would raise that capital, such as by selling assets, going to the capital markets or appealing for further state aid.

Eurobank, now under state control, faces the biggest shortfall and needs €2.9 billion in capital. Market leader NBG must raise some €2.2 billion, the central bank said.

Since then, Piraeus Bank, Alpha Bank and Eurobank Ergasias have all announced capital hikes; NBG, however, has said it can manage without raising fresh funding.

NBG said its fourth-quarter net interest income, which represents the bank's core revenue, was flat at EUR776 million compared with EUR772 million in the third quarter.

Greek banks are hoping that as Greece's economy emerges from recession later this year, the volume of bad loans on their balance sheets will begin to decline, helping to return them to profitability.

Write to Alkman Granitsas at alkman.granitsas@wsj.com.

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