Home prices continued to slide down as more and more homeowners face foreclosure.

Home prices in 20 major cities across the country fell 2.8 percent in May to the lowest levels in six years, according the S&P/Case-Shiller index released today.

The group’s 10-city index, which has a longer track record, fell 3.4 percent in May, the biggest drop since 1991.

Prices in Detroit fell the most, down by 11.1 percent, followed by San Diego, down 7 percent. On the other hand, home prices in Seattle increased the most by 9.1 percent, followed by Charlotte, N.C., up 7 percent.

Meanwhile, U.S. home foreclosure filings rose 58 percent in the first six months of the year and could surpass 2 million this year, according to RealtyTrac. At this rate, the online reporting service for foreclosure properties says there is one filing for every 134 households.