SAN FRANCISCO - Apple overtook Google's Android to become the leading smartphone platform in the United States in the fourth quarter of 2011, thanks to strong demand for its latest iPhone model, said a study released on Wednesday.

In the October to December quarter last year, Apple's share of the US smartphone market doubled from a year earlier to 44.9 percent, while Android's share fell from 50 percent to 44.8 percent in the same period, according to new data from market research firm Kantar Worldpanel.

While Android retains global smartphone crown, Apple is now growing at a faster rate, driven by the launch of its latest iPhone 4S model in October last year, Kantar Worldpanel noted.

"Overall, Apple sales are now growing at a faster rate than Android across the nine countries we cover," Dominic Sunnebo, global consumer insight director at the research firm, said in a statement.

Apple posted better-than-expected quarterly results on Tuesday, saying it sold a record-breaking 37.04 million units of iPhone in total in the fourth quarter last year, an increase of 128 percent over the year-ago period.