The world's largest insurer, AIG, has reported net income of $US3.09 billion ($3.32 billion) for the third quarter, a 27% decrease on the corresponding period last year.

AIG's general insurance unit had a combined ratio of 90.17% in the third quarter, against 89.1% for the previous period.

President and CEO Martin Sullivan says the company's results were affected by its exposure to the US subprime mortgage market.