Serbia withdrew its ambassadors from Washington and other major capitals as the United States and several European powers led international moves to recognize Kosovo's independence.
And in a speech to the United Nations Security Council, Serbian President Boris Tadic warned that backing Kosovo set a dangerous precedent that would threaten world order.
Their fears were to some extent reflected in President Tadic's address to the 15-member UN Security Council Monday.
"This arbitrary decision represents a precedent, which will cause irreparable damage to the international order," he warned.
"There are dozens of various Kosovos in the world and all of them lie in wait for Kosovo act of secession to become a reality and to be established as an acceptable norm," he added.
Other countries, including China, Romania, Russia and Spain, also said they opposed Kosovo's independence.
Spain, which has has long struggled with violence by militant Basque separatists, condemned the move, as nationalist parties in its Basque and Catalan regions issued statements hailing the news.
Romania, which has a significant Hungarian minority, also condemned the move, as did Cyprus, which is divided between the Greek and Turkish Cypriot populations.
EU foreign ministers meeting in Brussels were divided over how to respond to Kosovo's split from Serbia, which sparked wild celebrations in Pristina but riots in Belgrade.
The ministers said in a declaration that it would be for individual nations to announce their decisions.
But Kosovo's Prime Minister Hashim Thaci said he was confident there would soon be international approval.
US, British, French and Turkish diplomats exchanged letters with Kosovo's leaders in Pristina to establish formal diplomatic ties.
And on Tuesday, Australian Foreign Minister Stephen Smith issued a statement recognizing Kosovo's independence.
But he added: "Australia strongly urges the leaders of Kosovo and Serbia to demonstrate the resolve and political determination to settle their differences peacefully."
French President Nicolas Sarkozy sent a letter to Kosovo President Fatmir Sejdiu recognizing Kosovo as a "free and independent state."
British Foreign Secretary David Miliband said his country had also recognized Kosovo.
Germany, Italy and 14 other EU member states declared their intention to follow suit, while a number reserved judgment.
Serbia's Foreign Minister Vuk Jeremic, confirmed that Belgrade was withdrawing its ambassadors from countries which recognized Kosovo's secession.
Belgrade insists the mainly ethnic Albanian territory is part of Serbia and vowed to block Kosovo from membership of the United Nations and other international organizations to which it belonged.
As President Tadic appealed to the UN Security Council in New York, in Belgrade, Serbia's parliament met Monday in special session to "annul" the independence declaration.
More than 5,000 protesters gathered in the capital to demonstrate against independence and some groups smashed the windows of a McDonald's restaurant and threw rocks at the Turkish embassy.
In Kosovo itself, an explosion in the flashpoint town of Mitrovica, near the building where UN police and OSCE officers are located, shattered car windows but hurt no one.
Russia and Serbia failed again on Monday to persuade the UN Security Council to oppose Kosovo's declaration -- but nor has the Council given its stamp of approval to the independence process.
China, like Russia a permanent member of the Security Council, expressed "grave concern" over Kosovo's declaration, which triggered new tensions between the Chinese and Taiwanese governments.
"The unilateral move taken by Kosovo will lead to a series of consequences. China is deeply worried about its severe and negative impact on peace and stability in the Balkan region," foreign ministry spokesman Liu Jianchao said.
