Industry estimates put the cost of the damage caused by terrorist attacks on the World Trade Center and the Pentagon at billions of dollars.
Credit rating agency Moody's reported that total claims could be $10bn to $15bn. Insurers such as Swiss Reinsurance said that estimated losses have reached $2.8bn, while an analyst said claims could reach $30bn.
Germany's Munich Re, the world's largest reinsurer, was one of the first to estimate the likely cost, putting its liabilities at up to Eu1bn ($906.6m). The company said this would severely hurt profits.
Allianz AG, Europe's number two insurer, said its exposure would be about Eu700m ($635m). France's biggest reinsurer, Scor, estimated total claims to be between $10bn and $15bn.
Losses at the World Trade Center, which cost $750m to build in the early 1970s, are likely to be shared by US and international insurers and reinsurers.
The most expensive man-made insurance loss in US history occurred in April 1992 during the Los Angeles riots when $775m was paid out in damages.
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