NEW : Khamenei : Islamic establishment `` will never give in to coercive demands '' NEW YORK TIMES Troops beat demonstrators in Tehran square , sources say .
NEW : Khamenei : Islamic establishment `` will never give in to coercive demands '' NEW : Iran 's ambassador to Mexico says protesters want to `` impose a dictatorship '' `` They were waiting for us , '' one protester says of security forces . Troops beat demonstrators in Tehran square , sources say .