WASHINGTON, July 29 (Reuters) - Multiple U.S. states are jointly investigating bid-rigging allegations related to municipal bond derivatives, and bond insurer Security Capital Assurance Ltd SCA.N has received subpoenas from two states.

XL Capital (XL.N: Quote, Profile, Research) , a Bermuda-based insurer which has a 46 percent stake in Security Capital, disclosed in a regulatory filing that in June one of its subsidiaries received a subpoena from Connecticut's attorney general and an "Antitrust Civil Investigative Demand" from Florida's top legal officer.

A spokeswoman for Florida's attorney general confirmed on Tuesday that a subpoena had been sent to Security Capital.

"We have sent a subpoena to Security Capital Assurance Limited," Sandi Copes, a spokeswoman in Tallahassee for the attorney general, said. "We are part of the joint investigation."

Copes declined to detail the nature of the subpoena, saying it was against policy to discuss active investigations.

XL, in its filing with the Securities and Exchange Commission made late on Monday, said the documents were sent "in connection with a coordinated multi-state attorneys general investigation."

A spokeswoman from XL did not respond to requests for comment.

In November 2006, the federal government began a wide-ranging probe into how the winning bids were decided for derivatives used to invest municipal bond proceeds. Authorities were especially concerned that pricing had been for guaranteed investment contracts, or GICs, agreements typically offered by insurance companies that offer a rate of return for a set time period.

The Connecticut attorney general's office had no comment on the investigation.