BlackBerry's share price fell Monday morning after investment firm Goldman Sachs lowered the tech company's rating from "buy" to "neutral."

In a note to investors, Goldman Sachs analyst Simona Jankowski said the new Blackberry Z10 smartphone's U.S. launch on March 22 was "disappointing, with limited marketing and tepid sell-through at AT&T and Best Buy stores alike."

"While we thought the international launch was solid, the U.S. launch is critical for BlackBerry’s ultimate success," Jankowski wrote.

Goldman Sachs views the BB10 launch as essential to BlackBerry's ability to turn around its "declining market share trajectory," and Jankowski said she now gives the company a 20 per cent likelihood of being able to achieve that goal, down from the previous 30 per cent estimate.

"The disappointing launch of the Z10 at AT&T reduces our confidence that sell-through of the BB10 will be successful in the important U.S. market," she wrote in the note.

"Our retail checks at over 20 store locations since March 22, including at AT&T, Best Buy, and Radio Shack, revealed a surprising lack of marketing support and poor positioning of the product. We also saw limited advertising around the launch."

The note confirmed the product has been well received by sales associates and reviewers, but is simply not selling well, with most locations reporting less than 10 sales per day, and some as low as two or three per day.

BlackBerry shares were down 4.5 per cent to US$14.23 by around noon ET on the NASDAQ.