U.S. home prices continued their steady upward march in May, spurred by rising sales and a dwindling supply of available houses.

The Standard & Poor's CoreLogic Case-Shiller 20-city home price index increased 5.2 percent in May compared with a year ago. That is down from a 5.4 percent annual gain in April but still above last summer's growth rate.

Solid job growth and near-record low mortgage rates are spurring more Americans to buy homes. Yet the supply of available homes has fallen in the past year, forcing buyers to compete against each other.

Home prices are slowly edging back to their peak levels reached during the housing bubble a decade ago. After falling 35 percent from 2006 through 2012, the 20-city index is now just 8.8 percent below its peak.