Serbia’s main political opposition party is in disarray after the resignation of its leader.
Tomislav Nikolic stood down after hard-line colleagues in the Serbian Radical Party refused to back his call for closer EU ties.
Critics say signing the agreement would mean abandoning Serbia’s claim to Kosovo, regarded by many as the country’s spiritual and cultural heartland.
Nikolic lost out in a knife-edge presidential vote in February to his pro-western rival Boris Tadic.
Observers say since then Nikolic has tried to shed his ultranationalist image with a softer line on national issues along with populist pledges to battle corruption and boost the country’s living standards.
A ratification vote on the Brussels agreement is due to take place in Serbia’s parliament this week.