U.S. single-family home prices rose more than expected in May, still reflecting robust spring sales spurred by homebuyer tax credits, Standard & Poor's/Case Shiller home price indexes showed on Tuesday.

The 20-city composite price index rose 0.5 percent on a seasonally adjusted basis in May after an upwardly revised 0.6 percent gain in April, topping the 0.2 percent rise forecast in a Reuters poll.

This was the second straight monthly rise after declines in the prior two months.

While May's report on its own looks somewhat positive, a broader look at home price levels over the past year still does not indicate that the housing market is in any form of sustained recovery, David M. Blitzer, chairman of the Index Committee at Standard & Poor's, said in a statement.

On an unadjusted basis, prices jumped 1.3 percent in May, following April's 0.9 percent gain, which was revised up from an 0.8 percent rise. This was the second straight monthly gain after declines in the six previous months.

The 20-city index increased 4.6 percent in May from a year earlier, S&P said.

All of the increases surpassed forecasts found in Reuters polls, which called for a 0.2 percent seasonally adjusted rise and a 0.3 percent increase unadjusted, as well as a 4 percent annual gain.

Still, house prices are basically flat over the last seven months, Blitzer said. It still looks possible that the housing market might bounce along the bottom for the foreseeable future, before showing any real improvement that will filter through to the rest of the economy.

(Reporting by Lynn Adler; editing by Jeffrey Benkoe)