WASHINGTON (AP) - Home prices rose in June for the third straight month amid a burst of home-buying due to tax incentives that have since expired.

The Standard & Poor's/Case-Shiller 20-city home price index posted a 1 percent increase in June from May and was up 4.2 percent from a year ago. Home prices nationally were up 4.8 percent in the second quarter compared with the first quarter, largely due to government tax credits of up to $8,000 that caused sales to surge.

Seventeen cities showed price gains on a monthly basis. Prices in Seattle and Portland, Ore. were flat from a month ago, while prices in Las Vegas fell.

Nationally, prices have risen 6 percent from their April 2009 bottom. But they remain 28 percent below their July 2006 peak.