SAN FRANCISCO, California, United States?NPD Group on Wednesday reported that smartphones running on Google-back Android software unseated BlackBerry devices as top sellers in the United States during the second quarter of the year.

Android phones continued an "upward climb" in the US market, accounting for 33 percent of all smartphones purchased from the start of April through the end of June, according to the market tracking firm.

BlackBerry devices made by Canada-based Research In Motion were second with 28 percent while 22 percent of smartphone purchases were iPhones from Apple.

"While the Google-developed (operating system) took market share from RIM, Apple's saw a small gain this quarter on the strength of the iPhone 4 launch," said NPD executive director of analysis Ross Rubin.

The most popular Android phone was the Motorola Droid, followed by the HTC Droid Incredible and the HTC Evo 4G.

RIM hopes it will have a hit on its hands with a freshly-unveiled Torch smartphone running on its new BlackBerry 6 software.

"Blackberry 6 will soon offer features that have been popular in recently launched Android handsets, such as support for capacitive touch-screens and a WebKit-based browser," Rubin said.

"However, the Blackberry Torch lacks the large screen allure that has characterized the best selling Android devices at its price point," Rubin said.

The NPD report supports figures released this week by Nielsen Company showing that Android smartphones are gaining ground in a hot US market.

"While the iPhone has been the headline grabber over the last few years in the smartphone market, Google's Android (operating system) has shown the most significant expansion in market share among current subscribers," Nielsen said in a release.

BlackBerry handsets continued to rule with 35 percent of the market while iPhones were second with 28 percent at the end of June, according to the results. Android smartphones had grown to 13 percent of the market.

Smartphones capable of data connections such as e-mail and Internet browsing made up 25 percent of the US market at the end of June and Nielsen predicted they would surpass the number of feature phones by the end of 2011.