NEW YORK (Reuters) ? St. Paul Travelers Cos. and Bermuda-based Ace Ltd. today said they received subpoenas from federal prosecutors in a widening probe of a type of reinsurance that insurers might use to smooth their own earnings.

St. Paul said it will cooperate fully with the request by David Kelley, the US Attorney for the Southern District of New York, as did Ace. The property and casualty insurers are among at least eight companies asked this week by federal prosecutors to provide documents.

The subpoenas, related to a product known as finite reinsurance, indicate a broadening of probes into possible improper accounting. The U.S. Securities and Exchange Commission and New York Attorney General Eliot Spitzer have also issued many subpoenas related to the product, including to St. Paul and Ace.

Other companies that got similar subpoenas from Kelley's office included Assurant Inc. and Bristol West Holdings Inc. PartnerRe Ltd. Platinum Underwriters Holdings Ltd. RenaissanceRe Holdings Ltd. and XL Capital Ltd., all of Bermuda have been subpoenaed. All said they would cooperate fully.

Authorities are examining whether some non-traditional reinsurance products function as loans to help insurers cover up losses, and if they transfer enough risk.

Connecticut Attorney General Richard Blumenthal has said he has issued at least 20 subpoenas about the products.

Spitzer's investigation of American International Group Inc.'s use of the products led to an accounting review that caused the giant insurer to reduce five years of profits by $3.9 billion.

In afternoon trading on the New York Stock Exchange, St. Paul shares rose 13 cents to $39.06, and Ace shares rose 23 cents to $46.13.