By Marc Frank HAVANA (Reuters) - Cuban President Raul Castro on Saturday called on the United States to establish civilized relations with his country, recognizing a new tone in bilateral talks on secondary issues while reiterating that the country's political and economic system were non-negotiable. The United States and Cuba have appeared more positive of late as talks around immigration, postal services, disaster prevention and other security issues have taken place, with officials from both countries cautiously welcoming each other's pragmatism and seriousness in interviews with Reuters. Castro said that "a civilized relationship between both countries" was something "our people and the immense majority of U.S. citizens and Cuban immigrants desire." Castro's speech came just two weeks after he and U.S. President Barack Obama shook hands at a memorial for the late Nelson Mandela. U.S. and Cuban officials overcame a series of potentially divisive incidents this summer, including the interception of a shipment of Cuban weapons headed for North Korea, with mutual displays of prudent diplomacy rarely seen since the 1959 revolution that brought Fidel Castro to power.