U.S. home prices rose an unexpectedly robust 2.5 percent in April from the previous month, with at an annualized rate of 12.1 percent from a year earlier, according to the S&P/Case-Shiller home-price index released on Tuesday.

That 2.5 percent gain is the largest monthly gain in the history of the index. It compares with a 10.9 percent gain for annual figures in March, and a 1.1 percent month-to-month gain at that time.

Economists expected a 10.5 percent annual gain in April, according to Briefing.com, so the index beat expectations. They expected a much more modest 1.1 percent monthly gain for April, in line with previous months.

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A newly built single-family home that is sold is seen in San Marcos, Calif., Jan. 30, 2013. Privately owned homebuilders are seizing on a housing supply crunch to tap the stock market as more Americans, buoyed by an improving economy, seek to buy their first home or move into bigger premises. Photo: REUTERS/Mike Blake

In separate news, U.S. home builder Lennar Corporation (NYSE:LEN) reiterated its belief in a genuine housing recovery, even as mortgage rates rise.

“Our second-quarter results together with real-time feedback from our field associates continue to point towards a solid housing recovery,” Lennar CEO Stuart Miller said in a statement. “Demand in all of our markets continues to outpace supply.”

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Only Detroit saw declines in April, with San Francisco posting the strongest gain in home prices, at 4.9 percent. 

The S&P/Case-Shiller index is based on a survey of single-family home prices in 20 cities. The index has posted increases every month since February 2012.