SAN FRANCISCO, Jan. 5 (Xinhua) -- The rivalry between Google Inc. and Apple Inc. has heated up as the two Silicon Valley giants are foraying deeper into each other's strongholds to win control of the increasingly important smart phone platform.

    Google on Tuesday officially unveiled Nexus One, the first smart phone designed and sold by the company, representing its strongest challenge against Apple's popular iPhone.

A screen shot of the Google Nexus One smartphone, on the Android platform. Nexus One handsets are no thicker than pencils and no heavier than keychain Swiss Army knives, Google engineer Erick Tseng said while demonstrating one of the smartphones. (Xinhua/Reuters Photo) Photo Gallery>>>

    The new handset is an exemplar of what's possible with mobile phones on Google's Android operating system, Google executives said, claiming that it belongs in the emerging class of devices which the company calls "super phones."

    Nexus One is the first phone to be sold directly to consumers through Google's new web store, seen by the company as a new model for consumers to buy a mobile phone.

    Through the web store hosted by Google, consumers can buy NexusOne without service or purchase the phone with service from one of Google's operator partners.

    Nexus One is initially available from the Google web store in the United States without service for 529 U.S. dollars or starting at 179 dollars with a two-year contract from T-Mobile USA, Google said.

    Though it remains to be seen how Google's new way of distributing the handset will be received by consumers and wireless carriers, the adding of Nexus One into an expanding army of Android smart phones is putting Google into more direct competitions with Apple.

    Since the first smart phone running the Android platform debuted more than a year ago, 20 devices with 59 operators have gone on sale in 48 countries and regions, according to numbers released by Google.

    Although Android's share of the smart phone market is relatively small, market research firm Gartner has predicted that Android-based smart phones will capture 14 percent of the global market by the year 2012.

    Also as a reflection of the increasingly fierce competition between the two companies in the mobile arena, U.S. mobile advertising company Quattro Wireless on Tuesday confirmed that it has been bought by Apple for an undisclosed amount.

    Headquartered in the U.S. state of Massachusetts, Quattro is a competitor to AdMob, the Silicon Valley mobile ad company that Google intends to buy for 750 million dollars.

    It was reported that Apple had made a bid to acquire AdMob before it announced a purchase agreement with Google in November last year.