(Reuters) - Activist investor Carl Icahn said he had raised his stake in speech recognition software maker Nuance Communications Inc to 16.9 percent and that he may discuss the possibility of adding his nominees to the company's board. Icahn had reported a stake of 16.03 percent earlier this month. Nuance shares were up 2 percent in extended trading after closing at $18.31 on the Nasdaq on Thursday. Icahn said he had acquired the shares "in the belief that they were undervalued." (http://link.reuters.com/vaf72v) Apple Inc uses Nuance's speech recognition technology in its iPhone devices as part of its "Siri" voice feature. Following Icahn's announcement of a 16.03 percent stake earlier this month, Nuance adopted a stockholder rights plan to reduce the chances of any investor gaining control "through open market accumulation or other coercive takeover tactics without paying an appropriate control premium". The provisions would come into effect if a person or group acquires 20 percent or more of Nuance's shares in a transaction not approved by its board. The company was not immediately available for comment on Thursday. Nuance cut its full-year forecast earlier this month as some of its mobile customers had delayed contracts. Icahn, who is known for taking large positions in companies and pushing for management change, revealed on April 1 that he had taken a 9.27 percent stake in Nuance. (Reporting by Sruthi Ramakrishnan in Bangalore; Editing by Sreejiraj Eluvangal)