WASHINGTON — MetLife Inc. said Friday that the Securities and Exchange Commission has opened an investigation into potential improper trading of insurance contracts sold through the company's life insurance subsidiary.

MetLife said in its annual report that the SEC investigation is focusing on market-timing and late trading of a "limited number" of privately placed variable insurance contracts. The contracts were sold through MetLife's General American Life Insurance Co. unit.

MetLife previously disclosed that various regulatory bodies have contacted them to inquire about market-timing and late trading of mutual funds and variable insurance products.

MetLife reiterated that it is "fully cooperating" with the investigation.

A MetLife spokesman wasn't immediately available for comment Friday evening.

MetLife is the latest addition to a growing list of insurance and financial services companies that have reported federal or state investigations into rapid trading of variable annuity products, as well as other potential abuses involving their sales practices.

Last month, the National Association of Securities Dealers assessed another MetLife subsidiary, State Street Research Investment Services, with a $1 million fine for allegedly allowing improper trading of mutual fund shares. MetLife said that settlement, in which State Street neither admitted nor denied wrongdoing, resolved the NASD investigation.

The report was filed after the markets closed. Shares of MetLife ended down 26 cents at $35.41 on the New York Stock Exchange.