U.S. sales of existing homes fell 1.5 percent to an annual rate of 4.55 million units due to low inventory, the National Association of Realtors said Thursday, missing expectations and raising doubts about a housing recovery.

The result was down from a pace of 4.62 million units in April and below a forecast by economists surveyed by Bloomberg, who had expected a rate of 4.57 million sales. In positive signs, the May sales pace is 9.6 percent above the 4.15 million unit pace in May 2011 and the media price increased 7.9 percent to $182,600 on an annual basis.

The slight pullback in monthly home sales is more likely due to supply constraints rather than softening demand, said Lawrence Yun, NAR's chief economist, citing the 0.4 percent decline in inventory in May to 2.49 million units on the market.