"The settlement provides for an international representative to supervise the implementation," Ahtisaari said.
He added that a Nato-led peace force "will continue to provide a safe and secure environment... as long as necessary".
Ahtisaari declined to address the issue of Kosovo's ultimate status, saying this would be settled by the UN security council once he formally presents his plan, following a last round of consultations.
Serbia considers Kosovo, a province where ethnic Albanians, who are mainly Muslim, comprise 90 per cent of the province's 2 million people, as the medieval cradle of its statehood and religion.
"I am convinced that we will find a way to continue to defend the national and state interests" over Kosovo, Tadic said.
Serbia's foreign ministry also rejected Ahtisaari's plan, accusing the Finnish dilpomat of overstepping his authority and "changing the [international] status of the Republic of Serbia".
A ministry statement said the plan "dramatically changes the current state borders of Serbia" by allowing Kosovo to apply for membership in the United Nations and other international organisations.
Kosovo's Albanians welcome plan
Leaders of Kosovo's ethnic Albanian majority have however welcomed the UN plan saying that it "will end with independence" for Serbia's breakaway province.
"Kosovo will be sovereign like all other countries," Fatmir SejdiuKosovo , Kosovo's president, said after meeting Ahtisaari.
Agim Ceku, the prime minister and a former fighter in the Kosovo Liberation Army, said the document "is very clear for Kosovo's future".
The current UN plan does not mention independence for Kosovo, but includes provisions of statehood such as its own constitution, national symbols and possible membership of international organisations.
Kosovo has been run by the UN since 1999, when 11 weeks of bombing by Nato forced the late Slobodan Milosevic, Serbia's then leader, to withdraw Serb forces from the province.
Subsequently, some politicians have predicted violence and secession, or partition.
Both Nato and the current UN mission have made contingency plans for a such a crisis.