Fannie Mae, the largest provider of funding for US home loans, on Thursday said it would again tap the Treasury to plug a net worth

deficit after bad mortgages and foreclosure prevention efforts resulted in a $18.9 billion net loss in the third quarter.

Shares of Fannie Mae tumbled 7.1 percent after it reported results in extended after-hours trade.

Fannie Mae (FNM.P) (FNM.N) , which was seized by the government last year, said the quarterly loss stemmed from $22 billion in credit-related expenses, including charges on impaired loans it bought from mortgage-backed securities as it modified loans under President Barack Obama's foreclosure prevention plan.

The company also boosted its provision for credit losses in future quarters.