Social-networking star Facebook surpassed Google to become the most visited website in the US for the first time last weekowed.

Facebook's homepage finished the week ending 13 March as the most visited site in the country, according to industry tracker Hitwise.

The 'important milestone', as described by Hitwise director of research Heather Dougherty, came as Facebook enjoyed a massive 185% increase in visits in the same period, compared to the same week in 2009.

By comparison, visits to search engine Google.com increased only 9% in the same time, although the tracker does not include other Google sites such as Gmail, YouTube and Google Maps.

Taken together, Facebook.com and Google.com amounted to 14%of the entire US Internet visits last week.

Google has been positioning challenges in recent months to Facebook and the micro-blogging site Twitter by adding the social-networking feature Buzz to its Gmail service.

In what could signal an escalating battle between Facebook and Google, the leading social-networking service celebrated its sixth birthday earlier this year with changes including a new message inbox that echoes Gmail's format.

Facebook boasts some 400 million users while Gmail had 176 million unique visitors in December, according to tracking firm comScore.