Serbians were to protest en masse against Kosovo's declaration of independence in Belgrade on Thursday, a day after NATO-led peacekeepers blamed Serb leaders for unrest in the fledgling state.
Hundreds of thousands of people were expected to gather in front of the old Yugoslav parliament building in central Belgrade for the "Kosovo is Serbia" rally, including celebrities such as film director Emir Kusturica.
Serbian President Boris Tadic and Prime Minister Vojislav Kostunica have appealed for calm during the demonstration, which is due to begin 5:00 pm (1600 GMT).
Tadic meanwhile was to head to Romania, one of the few European Union states to back Belgrade's position that Kosovo's declaration of independence from Serbia at the weekend is a violation of international law.
Most Serbs bitterly oppose losing Kosovo, which they consider the cradle of their history, culture and Orthodox Christianity.
"We are struggling for what is legitimately ours. We will not tolerate this illegal act of secession," Serbian Foreign Minister Vuk Jeremic told European lawmakers in Strasbourg on Wednesday.
Romanian President Traian Basescu has rejected Kosovo's independence declaration as illegal, arguing that the move could set a precedent for other regions with separatist ambitions -- a point also made by Serbia and Russia.
Tadic was due to meet Basescu and the head of Romania's lower house of parliament, Bogdan Olteanu.
So far, 18 of the 27 EU member states have backed Kosovo's independence, either formally recognizing it or declaring their intention to do so. Cyprus, Romania and Spain have explicitly refused recognition.
In Kosovo, two border crossings with Serbia were reopened Wednesday, a day after being set alight by Serbs angered by Kosovo's independence declaration.
The commander of the NATO-led Kosovo Force (KFOR), General Xavier Bout de Marnhac, held leaders of Kosovo's minority Serb community responsible for the incident.
"Some local leaders took a huge responsibility yesterday," the French general said.
"The leaders should think deeply of their responsibility when they trigger this type of demonstration."
The border crossings at Banja and Jarinje were closed Tuesday after at least 1,000 Serbs from Kosovo and Serbia ransacked and torched the two sites.
Hardline Kosovo Serb political leader Milan Ivanovic hit back, calling KFOR "a servant of US interests" and accusing foreign forces of turning "Kosovo into a concentration camp."
The border crossing attack was the most violent reaction to the unilateral break by Kosovo and marked the first intervention by KFOR -- made up of 17,000 troops from more than 30 countries -- since independence.
Russian Foreign Minister Sergei Lavrov meanwhile denounced the EU's 2,000-strong "Rule of Law Mission" sent to train and mentor Kosovo police, judges and customs officials.
"There is a bitter irony even in its name -- a mission to uphold the law in violation of the supreme law, international law," Lavrov said.
In Strasbourg, Jeremic told the European Parliament's foreign affairs committee: "Relations between Serbia and certain members of the European Union have been compromised and I don't see how we can accelerate our efforts towards Europe."
Serbia, whose parliament declared the split illegal, is recalling its ambassadors from nations that recognize Kosovo's independence including Australia and the United States, and has fired off letters of protest.
In Vienna, the Organization for Security and Cooperation in Europe was due to discuss Kosovo on Thursday, the first day of its two-day parliamentary assembly.
