AIG has announced its intention to add $US4.1 billion ($4.09 billion) to the reserves of its property and casualty insurer Chartis.

The company says that strengthening Chartis’ loss reserves reflects adverse development on prior accident years in classes of business with long reporting tails.

Four classes – asbestos, excess casualty, excess workers’ compensation and primary workers’ compensation – represent about 80% of the total charge.

“The majority of the strengthening relates to development in accident years 2005 and prior,” AIG says.

The total reserve strengthening represents about 6% of the total general insurance liability for unpaid claims and adjustment expenses.