Sales of existing single-family homes declined in July while the stockpile of unsold homes grew. With concern mounting that a national housing bubble is on the verge of bursting, analysts and economists are closely eyeing home sales data for signs of a slowdown.

Data from the National Association of Realtors shows that existing home sales fell by 2.6% in July with only 7.16 million homes selling on a seasonally adjusted basis. In June, by comparison, 7.35 million existing homes were sold--and that represented a record high sales level. The decline was also noticeable in the condominium market, where sales also fell by 5% that month.

Regional performance varied. July home sales in the western U.S., for example, fell by 7.5%. Condo sales slowed down even more, with a 13% decline. Meanwhile overall home sales were only down 3.3% in the Northeast and 1.8% in the Midwest. The one exception was the South, which saw no change in existing home sales activity.