A British company responsible for 22% of the £2.3bn insurance covering the World Trade Centre has gone to court.
SR International Business Insurance is trying to prevent the Centre's owners defining the September 11 outrage as two attacks - and doubling its bill.
The firm says it's "prepared to honour its insurance obligations" for the attack that demolished the pair of 110-storey buildings, but will not pay twice because two planes were used.
The lawsuit, filed in Manhattan, seeks to deflate any expectations that an investor group led by Larry Silverstein might be entitled to twice as much money if the crashes are considered separate terrorist attacks.
Mr Silverstein, through his company Silverstein WTC Properties, manages World Trade Centre Properties.
SR International, a unit of reinsurer Swiss Re, says it's seeking a declaration from the courts that the damage to the Centre is one insurance loss - not multiple and unconnected losses.
It is also asking the court to decide whether it owes £510m solely to the investor group, or rather to other entities including businesses harmed by the disaster.
According to the court papers, the Port Authority local government agency entered into a 99-year lease with each of the World Trade Centre buildings on July 16, and with a separate company for the shopping mall.
The lawsuit says the insurance purchased for the properties was far below the projected £3.3bn necessary to replace the buildings and cover the group's rental income losses after a catastrophic loss.
It adds that a failure to rebuild the World Trade Centre towers and two other buildings would mean the port authority and lenders would be entitled to any insurance proceeds and Silverstein "would likely obtain only a fraction of the total insurance recovery".