Larry A. Silverstein, who has won nearly $4.6 billion in insurance payments to cover his losses and help him rebuild at the World Trade Center site, is seeking $12.3 billion in damages from airlines and airport security companies for the 9/11 attack.

Mr. Silverstein, the developer of ground zero, sought the damages, whose amount was not previously known, in a claim filed in 2004, that says the airlines and airport security companies failed to prevent terrorists from hijacking the planes used to destroy the buildings.

His case was consolidated last week with similar, earlier lawsuits brought by families of some victims of the attack and by other property owners. But in seeking $12.3 billion, he is by far the biggest claimant in the litigation.

The size of Mr. Silverstein’s claim was revealed last week at a status conference on the litigation in United States District Court in Manhattan.