A real state sign is seen near a row of homes in the Haight Ashbury neighborhood in San Francisco, California July 17, 2014. REUTERS/Robert Galbraith

NEW YORK (Reuters) - U.S. single-family home prices accelerated at a slower pace in April, falling short of forecasts, a survey showed on Tuesday.

The S&P CoreLogic Case-Shiller composite index of 20metropolitan areas rose 5.7 percent in May on a year-over-year basis from a upwardly revised 5.8 percent increase in April.

May’s result fell just short of the 5.8 percent increase forecast in a Reuters poll of economists.

David Blitzer, managing director and chairman of the index committee at S&P Dow Jones Indices, said the lean supply of homes was a key driver to the continued rise in prices. The inventory of existing homes for sale is around four months and new home construction remains subdued by historical standards.

Blitzer said the pace of gains varies significantly by market, which is unlike the pattern seen in the 2000-2006 housing bubble when rising prices were almost universal.

On a monthly basis, prices in the 20 cities rose 0.1 percent in May on a seasonally adjusted basis, the survey showed, short of expectations calling for a 0.3 percent increase.

On a non-seasonally adjusted basis, prices increased 0.8percent from April.