The S&P Case-Shiller U.S. home price index continued to deteriorate in May as the 20-city composite index posted a record annual decline of 15.8%. The Case-Shiller index has fallen every month since peaking in July 2006.

The month-over-month decline in home prices was 0.9%, compared to the 1.3% loss in the previous month. The 20-city composite is now at a level of 168.54.

"For the second straight month, all 20 [metro areas] posted annual declines, nine of which are posting record lows and 10 of which are in double-digits," the report said.

The 10-city composite, which also posted a record low with an annual loss of 16.9% in the report, is at 181.48.

"Regional patterns stand out: the Sunbelt led by Miami, Tampa, Phoenix, Las Vegas, San Diego and Los Angeles saw the biggest booms and now see the largest declines," said David Blitzer, chairman of the S&P's index committee. "The Northeast, including Boston and New York, is cyclical but less volatile while the Midwest, paced by Detroit and Cleveland face difficult local economies."

Miami and Las Vegas were the worst performers, falling by 3.6% and 2.9% in the month respectively. By contrast, Charlotte and Dallas have recorded three consecutive months of positive returns.

Blitzer said one bright spot is that seven metropolitan areas showed some improvement in their deterioration.

In April, the 20-city composite had fallen by 15.2% year-over-year while the 10-city composite had fallen by 16.2% from the previous year.

The S&P/Case-Shiller Home Price Indices measures the residential housing market, tracking changes in the value of the residential real estate market in 20 metropolitan regions across the United States.

By Patrick McGee and edited by Nancy Girgis