PARIS, May 25 (AFP) - At least 80 foreign journalists have been expelled by Belgrade, including some who were mistreated, and several Balkans' reporters jailed and censored, the press watchdog body Reporters Sans Frontieres (RSF) said Tuesday. The group denounced the slaying on April 11 of opposition journalist Slavko Curuvija, and called for the immediate release of both Croat journalist Antun Masle, held since April 20 by Yugoslav soldiers in Montenegro, and Serbian television director Soko Nebojsa Ristic, arrested on April 23 for protesting against censorship. It said the following foreign reporters were threatened or mistreated -- Lucia Annunziata, of RAI television and Il Messagero and Il Foglio, Catharina Nynke of The Netherlands Net 5, and Hungarian TV2 staff, Tvrtko Vuljity and Zolatn Gazsi. The group also denounced the fact that Pit Schnitzler, of Germany's SAT1 TV network, had been held in solitary confinement for a month and beaten each day. In Kosovo, where working conditions were extremely tough, Slovenian journalists Vili Einspieler and Tomi Lombar, as well as Finnish photographer Juha Metso, were beaten by paramilitary groups or Serbian police, it said.  