Serbian Prime Minister Vojislav Kostunica has said the European Commission's decision to call off talks on closer ties will damage his country.
PM Vojislav Kostunica urged Ratko Mladic (pictured) to surrender
The move came after Serbia failed to hand over fugitive war crimes suspect Ratko Mladic to The Hague tribunal.
The tribunal's chief prosecutor, Carla Del Ponte, says Serbian authorities knew where Mr Mladic was hiding and could have arrested him two weeks ago.
Serbia's deputy prime minister resigned over Mr Mladic's continuing liberty.
Miroljub Labus, a key negotiator with the European Union, said his government had "betrayed" the interests of the country and its citizens by not arresting Mr Mladic and failing to secure talks with the EU.
Mr Mladic, a former leader of the Bosnian Serb army, is accused of genocide in relation to the massacre of about 8,000 Muslim men and boys in Srebrenica in 1995.
The deadline set by the EU for his arrest expired on Sunday.
Prime Minister Kostunica said he was disappointed the EU had called off talks on preparations for EU entry, leaving his country in "very difficult circumstances".
Mr Kostunica, who had promised that Mr Mladic would be located, arrested and transferred to the tribunal, said everything had been done to try to bring in the fugitive.
He said Mr Mladic was "alone" on the run since the government had detained key people whom the former Bosnian Serb army leader relied on for support.
"His entire network has been uncovered; Mladic is now hiding all alone," he said.
Mr Kostunica also made a direct appeal to Mr Mladic, saying that Serbian military officers had always put the interests of the state and people above themselves. He said Mr Mladic was causing "grave damage on our state and national interests" by not surrendering to The Hague.
The BBC's Nick Hawton, in Belgrade, says these were strong words from the Serbian prime minister, but are unlikely to move the European Union, which has insisted Mr Mladic must be transferred to The Hague.
EU Enlargement Commissioner Olli Rehn said he was disappointed Belgrade had not detained Mr Mladic but had to call off the negotiations on the stabilisation and association agreement.
"The Commission is ready to resume negotiations as soon as Serbia accedes full co-operation," he said.
Ms Del Ponte said: "The obvious conclusion I can draw is that I was misled when I was told at the end of March that the arrest of Mladic was a matter of days or weeks."
Serbia was hoping to reach a new deal with the EU by July to take its first step on the road to eventual membership.
All the other countries in the Balkans, except Bosnia, already have such stabilisation and association agreements, providing for closer political and economic ties with the EU.
The fact that Mr Rehn has said talks are to be "called off" and not "suspended" means the EU executive can resume talks instantly once Mr Mladic is arrested - rather than go through the lengthy procedure of getting political approval from all 25 EU governments.
But there are fears of a nationalist backlash at a sensitive time in Serbia's political calendar.
This year, Belgrade stands to lose both the province of Kosovo, where the majority ethnic Albanians demand independence, and its federation partner Montenegro, which will be holding a referendum in just a few weeks on whether to continue in union with Serbia.