German insurance giant Allianz said Thursday natural catastrophes and losses on its investments in Greece slashed its bottom-line in half in 2011.

Allianz said in a statement it had booked net profit of 2.545 billion euros ($3.4 billion) last year, a drop of 49.6 percent from a year earlier.

The decline "was mainly due to very conservative writedowns of 1.9 billion euros from Greek sovereign debt and investments, particularly in financials," Allianz explained.

But at an operating level, the insurer insisted that it achieved its targets for 2011, "despite volatile financial markets and an unusually high level of natural catastrophes."

Operating profit fell by 4.6 percent to 7.866 billion euros and revenues were down 2.7 percent at 106.5 billion euros, the statement said.

"2011 was a tough year. But we maintained our stability throughout. That's an extraordinary achievement," said chief executive Michael Diekmann.

Looking ahead, "we are expecting similar global economic conditions in 2012 with a moderate improvement in the second half of the year," Diekmann said.

"The first steps to stabilise the eurozone have already been implemented successfully. We are confident about our strong business opportunities in 2012," he said.

Allianz was therefore raising its operating profit outlook to "8.2 billion euros, plus or minus 0.5 billion euros," the chief executive said.