The federal court battle over whether the destruction of the World Trade Center constitutes an insurance claim for one or two terrorist attacks involves a thorny question without precedent in U.S. law, say legal experts.

At issue is a request for a declaratory judgment, filed Oct. 22 in U.S. District Court in Manhattan, by a subsidiary of Zurich, Switzerland, reinsurance giant Swiss Re. It seeks to limit its payment obligations from the Sept. 11 action that crumbled the twin towers.

The Swiss Re unit, SR International, is an excess and surplus lines company chartered and based in the United Kingdom.

In the federal complaint, Swiss Re has asked the court to declare that the collapse of the twin towers constituted one insurable loss.