Serbian Prime Minister Vojislav Kostunica has warned the EU it will have to decide between an independent Kosovo or closer ties with Belgrade.
Mr Kostunica's comments come weeks before presidential elections
In a statement, he said EU governments would have to determine whether they wanted a "whole" Serbia as a partner or a "quasi-state on Serbia's territory".
Kosovo is expected to declare independence in the next few months.
EU foreign ministers will meet at the end of January to consider sending a police and justice mission.
Serbia strongly opposes the EU's plans and Mr Kostunica said that such support for the Serbian province's independence would be "like grabbing a part of Serbia's territory".
There have already been protests by ethnic Serbs in Kosovo against the police mission.
In November 2007, Serbia initialled a Stabilisation and Association Agreement, taking a first step towards membership of the EU.
But the Serbian prime minister said a full signing would not take place if the EU contingent was sent.
Serbia is facing presidential elections on 20 January and the future of Kosovo is likely to be an important issue in the campaign.