Apple Inc on Tuesday questioned recent data showing smartphones using Google's Android operating system surpassing iPhone sales in the United States, and said there are no signs that the competition is gaining in the smartphone market.

Smartphones using Android accounted for 28 percent of U.S. unit sales in the first quarter, ahead of Apple at 21 percent, research group NPD said on Monday. Research in Motion Ltd was No. 1 at 36 percent, NPD said.

Apple said the NPD data didn't provide a complete picture.

This is a very limited report on 150,000 U.S. consumers responding to an online survey and does not account for the more than 85 million iPhone and iPod touch customers worldwide, said Apple spokeswoman Natalie Harrison.

She said the iPhone far outsells Android on a worldwide basis, and pointed to a report from IDC last week which showed the iPhone with a 16.1 percent global market share, behind No. 2 RIM and No. 1 Nokia Oyj.

We had a record quarter with iPhone sales growing by 131 percent and with our new iPhone OS 4.0 software coming this summer, we see no signs of the competition catching up any time soon, Harrison said.

Apple has sold more than 51 million iPhones since it started selling the device in 2007.

Shares of Cupertino, California-based Apple rose 2.2 percent to $259.55 on the Nasdaq on Tuesday.

(Reporting by Gabriel Madway. Editing by Robert MacMillan)

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