Ms Del Ponte's comments heap more pressure on the Croatian government to arrest Ante Gotovina, accused of arranging the killing of at least 150 civilians and the expulsion of 150,000 others during an operation against the Krajina Serbs in 1995.
Satisfactory co-operation with the UN war crimes tribunal in The Hague is the one remaining obstacle to Croatia's ambition to launch membership negotiations with the EU on 17 March. This week, Olli Rehn, the European commissioner for enlargement, said if he had to make a recommendation on the basis of present information, "I could not recommend opening negotiations with Croatia".
Ms Del Ponte, whose judgment will be crucial, said bluntly: "The government of Croatia is in a position to arrange the transfer to The Hague." Officials believe that the general, who became a hero figure for nationalists, may be moving through the region. They say this would be impossible without a network of supporters on whom the Croatian authorities could easily exert pressure.
The EU's foreign policy chief, Javier Solana, underlined the importance of Ms Del Ponte's judgment, saying it "will be absolutely fundamental for the final decision". Diplomats believe the talks cannot open without a development, preferably the handover of General Gotovina.
Ms Del Ponte is also frustrated that 18 indictees remain free in the Balkans, the most infamous being Radovan Karadzic, wartime leader of the Bosnian Serbs and his general, Ratko Mladic. She added that no one would be able to commemorate the 10th anniversary of the Srebrenica massacre, in which around 7,000 Muslim men and boys were slaughtered, with those accused of responsibility remaining at liberty.