WASHINGTON (Reuters) - Sales of existing U.S. homes surged 4.5 percent in April to a record high, and home prices posted the biggest annual gain in almost a quarter century, a trade group said on Tuesday.

Sales of previously owned homes rose to a seasonally adjusted annual rate of 7.18 million units last month, the National Association of Realtors said. That figure includes both single-family homes and condominiums.

Single-family homes sales rose 4.5 percent in April to a 6.28 million unit rate from a 6.01 million unit rate in March. Condo sales climbed 4.8 percent to a 899,000 unit rate from an 858,000 unit pace in March.

The sales surge came as mortgage interest rates dipped.

"The record was basically unexpected, but low mortgage rates were unexpected as well," said David Lereah, chief NAR economist. "Prices are now becoming a concern. There's a speculative element in home buying now."

Analysts had expected overall sales to shade up to a 6.90 million unit rate from the previously reported 6.89 million unit pace.

The national median home price rose 15.1 percent to $206,000 from the same month a year ago, the NAR report showed. That price increase was the biggest since November 1980, when prices rose 15.6 percent, NAR said.