Shares in Clearwire, the telecommunications service provider, fell 12 per cent on Friday amid concerns that operational problems at Sprint Nextel could damage the prospects for the companies’ mobile broadband partnership.

The drop comes as pressure mounts on Gary Forsee’s hold on the chief executive job at Sprint Nextel, the third largest US mobile carrier, in the face of complaints from dissident investors and reports that the company’s board has begun a search for a successor.