PALO ALTO, California: Facebook saw its growth rate slow dramatically in the US in June 2010, prompting suggestions the world's biggest social network might be reaching saturation point in the country.

According to a report from specialist online operator Inside Facebook, the Web 2.0 service attracted just 320,800 new visitors last month, compared to 7.8 million in May.

More specifically, this substantial decline was largely attributable to a significant contraction among the site's core 18-44 year old target audience.

Usage in the 45–54 year old age group, and their counterparts aged between 13 and 17 years old, remained essentially static.

Privacy issues may be one factor behind the trend, but Inside Facebook's study posited cited other, less controversial, reasons.

"In the years we've been tracking the demographic data, we've rarely seen a dip like this, so we would tend to favor the idea of a root cause," the organisation's study said.

"It's possible this is just a seasonal breather, as many students aren't in school and sharing as much content with each other as they do during the academic year, and some people may be on summer vacation."

Elsewhere, however, an assessment of these figures by Wired, the influential technology title, said Facebook could have exhausted the basic growth options available in its home market.

"If Facebook has hit its peak in terms of US users, the company will have to turn its attention to finding ways to make money off the site, not just add more users," Wired's analysis stated.

Given its exponential expansion to date, Wired also warned that the only way for Facebook to go was down.

"Users are finicky, and. Facebook could find itself caught in a battle of just trying to retain users who might jump ship to Google's rumored new network, or who just decide they are tired of maintaining a social networking profile," it argued.

Data sourced from CNN/Inside Facebook; additional content by Warc staff