"The unilateral declaration of Kosovo independence and the support of this process by other members of the international community would be illegal and Russia will not support it," Putin told a news conference after talks with his Bulgarian counterpart Georgi Parvanov in Sofia.
The Albanian-dominated Serbian province has been a UN protectorate since the NATO bombing of the former Yugoslavia ended a conflict between Albanian and Serb forces in 1999.
Most Western states back the volatile area's drive for independence, and recently agreed that Kosovo's status would be determined by the European Union and NATO. Russia insists that Belgrade and Pristina continue to seek a compromise.
Kosovo's newly elected Prime Minister Hashim Thaci earlier said Pristina's independence was an accomplished fact and would be declared as soon as the United States and the European Union were ready to recognize it.
Serbian President Boris Tadic, who attended the UN Security Council meeting on Wednesday, called upon the council to abide by its own resolutions and the United Nations Charter. UN Resolution 1244, adopted in 1999, reaffirmed the sovereignty and territorial integrity of the former Federal Republic of Yugoslavia to which Serbia is now the recognized successor state, and established that Kosovo was to remain part of Serbia.
Throughout long-running talks aimed at finding a solution to the status of Serbia's breakaway province, Russia has backed Belgrade in opposing Kosovo's sovereignty, warning it would have a knock-on effect for other secessionist areas, such as Transdnestr in Moldova, South Ossetia and Abkhazia in Georgia, and Nagorny Karabakh in Azerbaijan, so-called frozen conflicts since the 1990s.
Russian Ambassador Vitaly Churkin reiterated on Wednesday that the future of Kosovo was a Security Council issue and said council members should prepare a roadmap that would provide solutions to overcome the differences in approaches to Kosovo's status.