Amlin estimates its net losses from the US terrorist attacks at $45m (£30.82m) before tax.
Chairman Roger Taylor said the losses equated to about 16p per share after tax for the group, which operates at Lloyd's.
He said in a statement: “At this stage, it is very difficult to assess with any certainty the likely level of claims that will materialise but our view is that these events taken together will be the largest insurance loss on record.
"Amlin's business includes the insurance of property and transport and our underwriting skills have been developed so that we can offer our customers protection against the risk of catastrophe.
“These terrorist attacks represent a major loss by any historic measure but one which I believe will yet again demonstrate that the insurance industry has the ability to stand firm in support of its customers when they need us most of all.
“The challenge and opportunity now facing the insurance industry is to determine insurance programmes that not only accurately define the modern day risk but also rate them realistically."
He predicted better times for underwriting, but warned the company would make no interim dividend payment until the full year figures were available.
