American International Group (AIG) has decided to pursue a spin-off of its mortgage insurance business, according to people familiar with the matter, in a move that would come as the US insurer fends off activist investor Carl Icahn.

The spin-off of that business however, which accounted for 7.4 per cent of AIG's pre-tax operating income in the first nine months of 2015, is unlikely on its own to appease Icahn, who is calling for AIG to break up into three separate businesses.

The mortgage insurance business had revenue of $791 million in the first nine months of 2015.

AIG is expected to discuss the future of the mortgage insurance business on Tuesday, when it releases its strategic plan, and the sources said this week the company will pursue a partial spin-off of the asset.

This would mean that AIG shareholders would only receive some of the shares of the spun-out company, with the remainder kept by AIG itself.

The company is also expected to update investors on the sale of its Advisor Group division on Tuesday, as well as other initiatives aimed at winning shareholder support, the sources said.

The sources cautioned that details were still being finalized and asked not to be identified because the deliberations are confidential.

"AIG continues to take steps to narrow its focus, improve its financial performance, and return capital to shareholders. AIG maintains an active dialogue with shareholders, including Carl Icahn," the company said in an emailed statement.

Icahn wants AIG to become a smaller, simpler company and to shed its label as a non-bank Systemically Important Financial Institution (SIFI) - a tag that comes with enhanced regulation from the U.S. Federal Reserve.

However, AIG and its CEO Peter Hancock have resisted Icahn's call to split the insurer into three separate divisions.

Icahn disclosed in November that he owned a 3.4 per cent stake in AIG, making him the insurer's fifth-largest shareholder, according to Thomson Reuters data.

Other businesses that AIG may consider shedding include its Valic arm, which manages retirement money for teachers, and its life and annuity unit Sun America.

AIG's near collapse in 2008 and US government bailout was the driving force behind the inclusion of certain non-banks as SIFIs.

Pressure across the insurance industry to slim down was highlighted earlier this month when MetLife, the largest US life insurer, said it would split a substantial portion of its U.S. retail business from the core company due to the "regulatory environment".

AIG's cost structure has remained a cause of concern for investors, and its underwriting operations have suffered from falling rates for commercial property and casualty insurance.-Reuters