By Oana Lungescu
BBC News, Belgrade
The European Union has told Serbia it faces great opportunities but also great responsibilities, weeks after inconclusive parliamentary elections and just days after the UN envoy Martti Ahtisaari tabled a plan offering self-rule for the breakaway province of Kosovo.
After talks in Belgrade with President Boris Tadic and the outgoing Prime Minister Vojislav Kostunica, the EU foreign policy chief Javier Solana welcomed what he called the will of the government and people of Serbia to get engaged in talks on the future of Kosovo.
Nato peacekeepers have been in Kosovo since 1999
He also suggested the EU would not oppose a 10-day delay in the talks, as requested by Serbia to give time for the constitution of a new parliament and negotiating team.
"If that requires a certain adjustment in the calendar," Mr Solana said, "I'm sure Mr Ahtisaari will do it."
"We know Kosovo is not a very easy issue," said the German Foreign Minister Frank Walter Steinmeier, whose country holds the rotating presidency of the EU.
"We have respect for the responsibilities shouldered by the Serbian leaders, but we've come to say that Europe vests its hopes in Serbia. We want Serbia to take its place it deserves, you belong in Europe."
You do not have to go far in Belgrade to see how difficult it is for Serbs to let Kosovo go.
The government building where Prime Minister Kostunica now has his office was bombed in the spring of 1999, during the Nato air campaign that drove Serb security forces from Kosovo, where the overwhelming majority are ethnic Albanians.
Across the street looms the massive headquarters of the former Yugoslav army, still in ruins years after it too was targeted by Nato raids.
Some Serbs pledge to never surrender Kosovo
With characteristic irony, Serbs call this "smoke alley".
The presidency building offers another poignant reminder of the central place Kosovo takes in Serbia's history.
In the colonnaded room where President Tadic stood shoulder to shoulder with the senior EU officials, the fresco on one wall shows the battle of Kosovo of 1389, when Serbian armies were defeated by the Ottoman Turks.
While both Mr Tadic and Mr Kostunica have rejected the Ahtisaari plan, they struck a very different tone.
To the surprise of his EU guests, Mr Kostunica launched into a long speech, criticising Mr Ahtisaari for straying from his mandate and granting Kosovo "virtual independence."
While offering Kosovo the highest degree of autonomy, Mr Kostunica insisted Serbia would stand very firm and would not give up its territorial integrity and sovereignty.
"There can be no exception for any country, Serbia included," Mr Kostunica declared.
Mr Kostunica (l) is critical of UN plans for Kosovo self-rule
On the other hand, Mr Tadic, who met the UN envoy last week, made clear Serbia would defend its integrity and sovereignty, but did not want to obstruct the negotiation process.
Both men will have to reach a common stance, however, if a pro-Western government is to be formed in Serbia in the next weeks or months.
The EU enlargement commissioner Olli Rehn told Serbian leaders they had no time to lose.
"A new government can make a new start towards Europe," Mr Rehn said.
Its challenge will be double - not just to deal with the future of Kosovo, but also to set Serbia back on a track to Europe.
Last May, the EU froze talks on a Stabilisation and Association Agreement - which offers closer ties and unlocks the way to eventual EU membership - after the chief prosecutor of the UN war crimes tribunal Carla del Ponte accused the government of going back on its promises to catch Gen Ratko Mladic, one of the top war crime suspects from the Bosnian war.
Gen Mladic's capture is no longer seen as a pre-condition for the resumption of talks with Belgrade.
Instead, Mr Rehn said it would determine "the pace and conclusion of the talks".
The EU, he said, was ready to consider resuming the talks once the next government made a clear commitment to co-operate with the tribunal and took "concrete and convincing action and makes the structural changes" to catch all the remaining fugitives.
So Brussels will be scrutinising carefully who gets the key posts of interior and defence ministers in the new coalition and whether there are any changes among the intelligence and military chiefs that are believed to shield Gen Mladic.
Next Monday, EU foreign ministers are expected to give Mr Rehn a loose mandate to resume talks once Serbia does the necessary.
Italy, Spain and many others have argued that Belgrade should not be left isolated at such a delicate moment, while Britain, France and the Netherlands are reluctant to write what they see as a blank cheque.
But their margin of manoeuvre appears limited, especially after the same countries accepted late last year, under considerable American pressure, to include Serbia in Nato's Partnership for Peace programme.
The ultimate incentive for Serbia to play a constructive role on Kosovo is a clearer prospect of EU membership.
"Serbia and Kosovo aren't in the Pacific, so Europe is very engaged," Javier Solana said.
"Without Serbia in the EU, there won't be stability in the Balkans."