Diplomats say the European Union is likely to open membership talks with Croatia in March, if Zagreb fully cooperates with the United Nations war crimes tribunal.
The talks appear to depend on whether Croatia does more to find and arrest former General Ante Gotovina.
Last month, tribunal chief prosecutor Carla del Ponte criticized Croatia's efforts to catch Mr. Gotovina, who is accused of ordering the massacre of Croatian Serbs in 1995.
Reuters news agency quotes a Croatian diplomat as saying Zagreb is "not happy" with the condition for starting membership talks.
EU leaders are expected to make a formal decision on Croatia at a summit meeting that begins this Thursday.
Some information for this story provided by AP and Reuters.