WASHINGTON — Americans stepped up their homebuying for a third straight month in July, as sales accelerated to the strongest pace in eight years.

The National Association of Realtors said Thursday that sales of existing homes rose 2 percent last month to a seasonally adjusted annual rate of 5.59 million, the fastest rate since February 2007.

Sales have jumped 9.6 percent over the past 12 months, while the number of listings has declined 4.7 percent.

The housing market contains a mere 4.8 months’ supply of homes, meaning that prices are rising for an increasingly narrow set of properties. The median home price climbed 5.6 percent over the past 12 months to $234,000. Just 28 percent of the purchases last month went to first-time homebuyers, a group that historically accounted for 40 percent of sales.

“When first-time homebuyers compete with people who are more qualified borrowers that have additional cash, they tend to lose,” said Budge Huskey, CEO of the real estate brokerage Coldwell Banker.