Allianz increased its estimate of losses from the US terrorist attacks by 50% to Euro1.5bn (£920m).
It was the second increase by the German insurance group.
It originally estimated claims from the 11 September attacks would result in net costs of Euro700m (£430m).
The company's share price fell by about 3%.
But the company also announced a lower than expected loss of Euro46.3m (£28.4m) for the third quarter of the year.
The loss surprised analysts who had predicted a loss arising from the company's new acquisition, Dresdner Bank.
Dresdner contributed a profit of Euro313.8m (£192.7m) along with the group's property and casualty business.
Within the property and casualty business, the group's operations in Great Britain generated gross written premiums of Euro1.898bn (£1.165.4bn) in the first three quarters of the year.
The combined ratio improved from 116.9% at the end of December to 106% on 30 September, a change put down to improvements in motor insurance.
The group is sticking to an earlier full year net profit forecast of Euro1.7bn (£1.04bn). It expects premium income to increase by about 7%.
It said premium income for the first nine months of the year rose by 8% to Euro54.9bn (£33.7bn).
Hosted by comedian and actor Tom Allen, 34 Gold, 23 Silver and 22 Bronze awards were handed out across an amazing 34 categories recognising brilliance and innovation right across the breadth of UK general insurance.
