BlackBerry's shares tumbled the most since 2000 after the company reported a surprise loss and weak sales of a new touch-screen model, underscoring its challenges in competing directly with the iPhone and Android devices.

The company shipped 6.8 million smartphones last quarter, including about 2.7 million new BlackBerry 10 models - primarily its flagship Z10 touch-screen phone. Analysts had estimated total shipments of 7.5 million, with about 3.6 million BlackBerry 10 units. The company, based in Waterloo, Ontario, also blamed Venezuela's currency controls for a portion of its quarterly loss because they hurt Latin American revenue.

BlackBerry is struggling to expand beyond keyboard phones, which are still popular among some lawyers and other professionals but not as sought-after as Apple Inc's iPhone or smartphones based on Google Inc's Android. Last week's stock tumble more than wiped out its gains for the year, signaling investors may have been too optimistic about BlackBerry's ability to wage a comeback fight against touch-screen rivals.