Sales of the new BlackBerry in the UK have been better than expected, according to the chief executive of Canadian maker Research In Motion (RIM).

However, Thorsten Heins added that he is disappointed the device will not be released in the United States until mid-March. He said the US and its phone carriers have a rigid testing system.

He said: "We need to respect that. Am I a bit disappointed? Yeah, I would be lying saying no. But it is what it is, and we're working with all our carrier partners to speed it up as much as we can."

RIM unveiled new BlackBerrys last week after excruciating delays allowed Apple, Samsung and others to build commanding leads in the industry. Its shares fell 12% after Wednesday's launch, despite positive reviews about the new BlackBerry 10 operating system.

The first device in the new crop of the much-delayed revamped BlackBerrys on the US market will be the touchscreen Z10.

Mr Heins said a substantial number of UK users are moving from other platforms to BlackBerry and said that is an encouraging sign because they first targeted BlackBerry users.

He said: "It's beyond expectations. White is sold out already. The black is hard to stock up again. It's very encouraging. I won't share the number because I need to verify it, but we are getting a substantial number of users moving from other platforms to BlackBerry. That is an interesting data point."

Mr Heins, who a year ago replaced long-time executives who had presided over BlackBerry's fall, said he is confident that BlackBerry can become the third ecosystem behind Apple and phones running Google's Android operating system.