Kostunica did not specify who suggested such conditions. But his strong words come as international negotiators discuss the future of Kosovo, the province in southern Serbia populated mainly by independence-seeking ethnic Albanians.
Serb forces cracked down on ethnic Albanian separatists in the late 1990s until a NATO air campaign halted the fighting in 1999. Serbia was forced to hand control of Kosovo over to a U.N. mission and NATO peacekeepers.
The future status of Kosovo, a de facto protectorate for the past seven years, is being decided under the auspices of the so-called Contact Group - United States, Britain, Germany, Russia, France and Italy - in talks chaired by a U.N. envoy.
The next round of talks Aug. 7-8 is expected to focus on local reform and minority rights. The mediators have sought to resolve some issues in the troubled province before making a crucial decision on its future status.
Kostunica said Kosovo should enjoy "substantial autonomy" in running its own affairs, but within Serbia's borders, acording to the AP.
Kosovo's ethnic Albanian representatives insist on full secession from Serbia and are counting on Western support in gaining recognition as a new, independent state.
But Kostunica's government has been under pressure at home. Ultranationalist Serbian Radical Party leader Tomislav Nikolic recently said Serbia should "fight for Kosovo" if the province gains sovereignty, the AP reports.
The prime minister said Serbia will contest any attempt at Kosovo secession, and "will continue to regard it as its integral part" regardless of an outcome of the negotiations.