WASHINGTON (AP) — U.S. home prices rose steadily in May, pushed higher by a healthy increase in sales this year.

The Standard Poor’s/Case-Shiller 20-city home price index increased 4.9 percent in May from 12 months earlier, down slightly from a 5 percent pace in April, according to SP Dow Jones Indices.

Home sales have jumped in recent months as an improving economy boosts hiring and enables more people to afford a purchase. Yet the higher sales haven’t encouraged more people to sell their homes, leaving supplies tight and driving up prices.

Prices are soaring higher in some cities: They rose 10 percent from a year ago in Denver, 9.7 percent in San Francisco and 8.4 percent in Dallas. Washington, D.C. posted the smallest increase at 1.3 percent. Prices rose in all 20 cities from a year earlier.

The Case-Shiller index covers roughly half of U.S. homes. The index measures prices compared with those in January 2000 and creates a three-month moving average. The May figures are the latest available.

Sales of existing homes increased 3.2 percent in June to a seasonally adjusted annual rate of 5.49 million, the National Association of Realtors said last week. That is the fastest pace since February 2007. Sales are up from an annual pace of just 4.8 million in January.

Some of the accelerated pace has likely been driven by higher mortgage rates and an expected decision by the Federal Reserve to start raising short-term interest rates this year. Most economists forecast that decision will occur in September.

Yet the supply of available homes hasn’t kept up with rising sales. The number of homes listed for sale rose 0.4 percent in the past year, the Realtors said, while sales have increased 9.6 percent.

That has led to aggressive efforts by buyers to grab homes: The typical property was on the market for just 34 days in June, down from 40 in May and the shortest time since the Realtors’ group began tracking the data in May 2011.