A big jump in the supply of homes for sale was likely behind the small gain in sales from April. There were 1.54 million units available at the end of May, an increase of over 20% from May of last year. At the current sales pace, that represents a 4.6-month supply, which is still historically on the light side.

The median U.S. home-sale price reached a new record of $396,500 during the four weeks ending June 15, according to a report from real estate brokerage Redfin. This is a 1 percent increase compared to the same time last year, even though overall activity in the housing market remains low.

Home sale prices are at a record high, but buyers are nevertheless paying below sellers' asking prices, research shows.