Existing-home sales rose for the third straight month in September, according to the latest monthly report from the National Association of Realtors.

Sales of single-family homes, townhomes, condominiums and co-ops increased 11.3 percent last month to a seasonally adjusted annual rate of 4.91 million. Existing-home sales have been rising by double digits on an annual basis since July. On a monthly basis, sales fell 3 percent in September, compared with a 7.7 percent rise in August.

Nationwide, existing homes sold for a median $165,400 last month, down 3.5 percent from September 2010. Distressed homes, typically sold at discount, accounted for 30 percent of sales last month (18 percent were foreclosures, 12 percent were short sales), down from 35 percent a year ago, the report said.

Unsold inventory fell 2 percent in September to 3.48 million -- an 8.5-month supply at the current sales pace.

All-cash buyers, most of whom are investors, accounted for 30 percent of purchases last month, up slightly from 29 percent in September 2010, according to a separate NAR survey. Investors accounted for 19 percent of sales last month, up from 18 percent a year ago. First-time buyers made up 32 percent of sales.

Nationwide, sales rose on an annual basis in all price ranges last month, with homes under $100,000 seeing the biggest jump, according to the NAR report.