"It is unfortunate that we have been forced to sue to enforce our rights," World Trade Center developer and leaseholder Larry Silverstein says. "We are confident of our legal position that crashes of two separate planes into two separate towers at two separate times entitle us to claim that there was more than one occurrence within the meaning of our insurance contracts."

A spokeswoman from Travelers said the company has not yet seen the lawsuit and therefore would not comment. Travelers, Swiss Re and more than 20 other companies insured the World Trade Center in a $3.6-billion "per occurrence" policy. Swiss Re filed suit against WTC developer Silverstein in October, claiming the Sept. 11 bombings constituted a single occurrence. Silverstein countersued shortly thereafter.

Silverstein's attorneys now say they plan to ask the court for permission to amend their counterclaim in the Swiss Re suit to include as defendants nearly all of the more than 20 WTC insurers following a breakdown in settlement negotiations. Excluded from the amended list are insurers ACE Bermuda and XL.