Swiss Re has accused the US property magnate Larry Silverstein of "deliberately" underinsuring the World Trade Centre towers destroyed in the 11 September terrorist attacks.

Swiss Re, the reinsurance company that is leading the legal case against Mr Silverstein, said it had uncovered new evidence showing Silverstein Properties decided to buy less cover for the World Trade Centre than would be required to rebuild them because it wanted to cut costs.

This was despite Mr Silverstein's assertion after the 11 September attacks that he should be compensated for the full sum that reconstructing the towers would cost.

Jacques Dubois, the chief executive of Swiss Re's American arm, said: "In our view, Silverstein Properties knowingly and deliberately underinsured the WTC complex. We believe the record establishes that in order to save on premium dollars, Silverstein intentionally refused to insure against the risk of loss in excess of $3.5bn."

Mr Dubois added: "Rather than face this uncomfortable fact, Silverstein has led an aggressive media campaign aimed at rewriting history and inappropriately seeking to obtain funds in excess of the coverage he purchased."

The row broke out between Mr Silverstein and his insurers, which include a number of Lloyd's of London companies, after they disagreed about whether the terrorist attacks of 2001 constituted one or two events. The insurers said the onslaught was one event, enabling Mr Silverstein only to claim a total of $3.5bn, the upper limit on his policy.

Mr Silverstein countered that as there were two planes, there had been two attacks, so he should be allowed to claim on his policy twice, bringing in compensation of up to $7bn.

The two sides are fighting it out in the US courts in a case which is expected to drag on for many months.

In the meantime, the insurers are trying to counter negative publicity that they are not prepared to honour their policies covering one of America's one famous landmarks, which was devastated by terrorists.

Mr Silverstein has also attracted criticism for his handling of future plans for his ruined real estate, which he bought a 99-year lease for just one month before the terrorist attack. A spokesman for Mr Silverstein denied he had set out to save on insurance costs by not buying enough cover, saying: "The only hoax we see here is the one being perpetrated by Swiss Re. As we have said over and over, this was the largest insurance programme ever put together for a single group of buildings."

The insurers would like Mr Silverstein to give up his lease on ground zero and hand the land over to the New York authorities in return for a different lease on property near La Guardia airport. The insurers would then be prepared to broker a settlement with city's authorities.