MetLife Inc , the No. 1 U.S. life insurer, said on Thursday it posted a quarterly loss, hurt by investment losses, some of which were tied to improvement in the company's own credit spreads.

It was the third consecutive quarterly loss for the New York-based insurer, which suffered its fair share of pain from the credit crisis.

But MetLife's operating results in the latest quarter matched Wall Street expectations and the results showed growth in sales across most of MetLife's business operations, both in U.S. and international markets.

The company's shares fell about 1.5 percent after the report.

The net loss was $650 million, or 79 cents a share, compared with a profit of $600 million, or 83 cents per share, in the year-ago quarter.

Operating results rose 18 percent to $718 million, or 87 cents a share, matching analysts average expectations, according to Thomson Reuters I/B/E/S.

The net loss included $1.4 billion in after-tax net realized investment losses, including about $582 million in derivatives losses tied to improvement in the company's own credit spreads.

Under accounting rules, when its own credit spreads improve, MetLife has to record a decline in the value of its insurance liabilities. This also led to a loss in the second quarter.

Our businesses are performing well as evidenced by increased sales in a number of product areas in both the U.S. and internationally, said Chief Executive Robert Henrikson, in the earnings report.

U.S. annuity deposits were $4 billion in the quarter, including a 19 percent increase in fixed annuity deposits. MetLife also recorded increased premiums, fees and other revenue in its group life and nonmedical health divisions.

Overall, MetLife's quarterly premiums, fees and other revenue were flat at $8.5 billion.

Book value, a key valuation measure for investors, rose 27 percent from the end of June to $38.95 a share.

The company's shares, which rose 7.85 percent to close $36.84 in the regular session, fell about 1.5 percent to $36.28 after the report. The stock has more than tripled since its 52-week low of $11.37 in March when credit crisis worries stoked investor fears over life insurers' capitalization.

(Reporting by Lilla Zuill; editing by Andre Grenon)