"Such an idea is an insult to all those who endured the Golgotha of Goli Otok, where prisoners were subjected to the worst mental and physical torture for the sake of re-education and where between 3,800 and 5,000 people lost their lives," Radin said at a press conference in Pula on Monday.
He said his concern was all the greater because the Mayor of Rab, Zdenko Antesic, and town councillors had expressed their support for the project.
Radin said he would propose that a memorial centre be built on the island in tribute to all prisoners, including 350 ethnic Italians.
Goli Otok was the site of a political prison where opponents to the regime of Yugoslav communist leader Josip Broz Tito were incarcerated.
Radin welcomed a proposal by the presidents of Croatia and Italy, Stjepan Mesic and Carlo Azeglio Ciampi, that sites of suffering in the Second World War and after it should be marked.
"Through their initiative the two presidents certainly tend to overcome difficult historical periods, which should not be politicised but left to historians," Radin said.
Responding to a journalist's question, Radin said he would vote for the incumbent president, Stjepan Mesic, at the forthcoming presidential election, but stressed that he could not impose his opinion on the Italian minority.