Need a mortgage this month? It’s going to be harder - and more expensive - to get one. In the past week, turmoil in the mortgage markets has caused increasing problems for home buyers in the Bay Area and around the nation.

Kurt Herrenbruck, a mortgage planner with Fishman Financial Group in Berkeley, saw one client’s financing evaporate in the space of three days last week.

“The client is well-heeled, with (a high credit score), and $500,000 in the bank, making an owner-occupied purchase with a 25 percent down payment,” Herrenbruck said. “He needs a no-doc loan (meaning he cannot provide documents to prove his income) because of an employment hiccup.”

American International Group on Thursday told investors the housing market would have to spiral to Depression-era levels before the insurer would be harmed by its exposure to the residential mortgage market.

The world’s largest insurer has exposure to subprime loans — those made to people with tainted credit — as a lender, investor in mortgage-backed securities and supplier of mortgage insurance. But AIG characterized its exposure as minimal and said it would take declines of 30 percent to 40 percent in home values to dent the market for mortgages with stronger ratings, where most of its holdings lie.

Long-term mortgage rates fell again this week mostly on news of disappointing job growth and an increase in jobless claims, Freddie Mac and Bankrate.com reported today.

In Freddie Mac’s survey, the 30-year fixed-rate mortgage sank to an average 6.59 percent from last week’s 6.68 percent, and the 15-year fixed-rate mortgage fell to 6.25 percent from 6.32 percent. Points, which are fees lenders charge for loan processing expressed as a percent of the loan, averaged 0.4 on the 30- and 15-year loans.

American International Group Inc. — which originates and insures mortgages, and is also a major investor in mortgage-backed securities — says the downturn in U.S. housing markets is hurting its business, but that the company’s exposure to subprime investments is limited.

In a Securities and Exchange Commission filing Thursday, AIG reported net income for the quarter was up 34 percent to $4.28 billion. That’s despite a 63 percent decline in profits from consumer finance, including mortgage lending, and a $255 million loss in capital markets.