WASHINGTON (AP) — U.S home prices climbed 6.3 percent in June from a year earlier, as affordability is becoming a greater obstacle for would-be buyers.

The S&P CoreLogic Case-Shiller 20-city home price index rose at a slightly slower pace than the 6.5 percent annual gain in May from a year earlier. But home values are increasing at more than double the pace of average wage growth, weighing down property sales despite the robust job growth.

Mortgage rates are also higher than a year ago, creating another price pressure. The National Association of Realtors said that sales of existing homes have declined for the past four months.

Home prices in three metro areas have increased by double digits in the past year: Las Vegas (13 percent), Seattle (12.8 percent) and San Francisco (10.7 percent).