Washington ? Home prices in major U.S. cities have risen for the first time in eight months, boosted by an annual flurry of spring buyers.

The Standard & Poor’s/ Case-Shiller home-price index reported Tuesday that prices rose in 13 of the 20 cities tracked. Washington, D.C., saw the biggest price increases, followed by San Francisco, Atlanta and Seattle.

Still, six metro areas are at their lowest levels in the nearly four years. Those markets are: Charlotte, Chicago, Detroit, Las Vegas, Miami and Tampa.

Last month, home prices in big metro areas sunk to their lowest since 2002. Since the bubble burst in 2006, prices have fallen more than they did during the Great Depression.

The index, which covers metro areas that include about 50 percent of U.S. households, rose 0.7 percent, the first increase since July. The index measures sales of select homes in those cities compared with prices in January 2000 and provides a three-month average price. The April data is the latest available.

David M. Blitzer, chairman of Standard & Poor’s index committee, cautioned that while the price index increase was a “welcome shift from recent months,” much of the improvement was likely because of the beginning of the traditionally busy spring and summer home-buying seasons.

A delay in processing foreclosures is also a factor. Homes in foreclosure sell at a 20 percent discount on average, which can hurt prices in neighborhoods. But many foreclosures have been delayed while federal regulators, state attorneys general and banks review how those foreclosures were carried out over the past two years.

Even with the increase, housing remains the weakest part of the U.S. economy.

Sales of previously occupied homes sank in May to a seasonally adjusted annual rate of 4.81 million. That’s far below the roughly 6 million sold in healthy housing markets. Since the housing boom went bust in 2006, sales have fallen in four of the past five years.