NEW YORK (Reuters) – Prices of U.S. single-family homes plunged a record 16.6 percent in August from a year earlier and plummeted more than 30 percent in Las Vegas and Phoenix, Standard & Poor's said on Tuesday.

Home prices in 20 major metropolitan areas fell 1.0 percent in August from July, according to the Standard & Poor's/Case-Shiller Home Price Indices.

S&P said in a statement its composite index of 10 metropolitan areas declined 1.1 percent in August from July for a 17.7 percent year-over-year drop, also a record.

"The downturn in residential real estate prices continued, with very few bright spots in the data," David M. Blitzer, Chairman of the Index Committee at Standard & Poor's, said in the statement.

A huge supply of unsold homes, tighter lending standards and record foreclosures have pushed down home prices, deflating a bubble from the early part of this decade.

For the fifth straight month, prices fell in every region on an annual basis, he said.

Both the 10-City Composite and 20-City Composite Home Price Indices have fallen from a year earlier for 20 consecutive months. In regions, annual returns worsened from last month's report, he said.

"As seen throughout 2008, the Sun Belt markets are being hit the most," he said.

Prices in Miami, San Francisco, Los Angeles and San Diego all dropped in excess of 25 percent, he said.

S&P noted one bright spot as the acceleration in decline was only moderate in August from July.