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Switzerland's central bank said it may have posted a record loss in 2010 as the euro's slump eroded the value of its currency reserves.

The shortfall amounted to an estimated 21 billion Swiss francs ($28.4 billion), the Zurich-based Swiss National Bank said at the weekend.

That's about 4 per cent of the size of the economy.

Exchange-rate-related losses were about 26 billion Swiss francs and gold reserves had a valuation gain of about 6 billion francs, according to the bank.

The SNB, led by Philipp Hildebrand, bought foreign currencies at an unprecedented pace in the first half of last year to fight franc gains, which threatened to hurt the recovery and spark deflation. While policy makers ended their intervention policy in June, Europe's debt crisis has since eroded the euro and pushed the franc to an all-time high last month.

"It is not the SNB's job to make profits but to ensure price stability," said Fabian Heller, an economist at Credit Suisse Group in Zurich.

"It's difficult to say what would have happened had they not intervened. Still, what we learn is how difficult it is to fight the markets."

Hildebrand said in Bern that while the franc is strong against practically all currencies, Europe's debt crisis is posing an enormous burden.

He didn't say whether the SNB is ready to reintroduce intervention.

SNB policy makers will act if needed to counter deflation or inflation threats, he said, adding that the central bank has a clear mandate.

The franc posted its biggest weekly decline against the euro in more than seven months last week. Still, it has appreciated about 4 per cent in the past two months, reaching a record 1.2402 on December 30.