Independence is "the only viable option" for Kosovo, the U.N. envoy for the province said in a report released Monday to accompany his proposal on the territory's future.

The two documents by Martti Ahtisaari, who mediated yearlong talks between ethnic Albanians and Serbs, were delivered to the U.N. Security Council on Monday. The council will make the final decision.

In the 3 1/2-page introductory report accompanying the proposal, Ahtisaari said he had "come to the conclusion that the only viable option for Kosovo is independence, to be supervised for an initial period by the international community."

It is the first time the envoy has explicitly mentioned independence for the Serbian province in an official document.

Ahtissari's plan faces an uncertain future in the Security Council, which is split on the issue. Russia supports Serbia — which vehemently opposes independence for Kosovo — and has implied it could use its veto power in the Council if Belgrade's interests are not addressed. The United States and the European Union back the U.N. plan.

A Russian diplomat at the U.N. in New York said Monday the mission was still studying the report and had no immediate comment on it. Speaking anonymously because he was not authorized to address the media, he said council members may hold informal talks on the proposal as early as Tuesday.

Diplomats at U.N. said the council would likely have its first formal discussion of the report April 3. The plan would grant Kosovo its own constitution, flag, anthem and army, as well as rights to minority Serbs to run their daily affairs. But while setting the stage for Kosovo's statehood, the text of the plan itself does not use the word "independence."

Kosovo has been administered by the United Nations since 1999, when NATO airstrikes ended a Serbian crackdown on ethnic Albanian separatists. An estimated 10,000 ethnic Albanians and 1,000 Serbs were killed during the 1998-1999 war.

Ethnic Albanians make up 90 percent of Kosovo's 2 million people and have been pressing for independence for nearly two decades. The U.N. plan is an attempt to resolve the final major dispute remaining from Yugoslavia's bloody breakup in the 1990s.

Stressing the urgency of the issue, Ahtisaari said that allowing the territory's status to remain ambiguous was a destabilizing factor.

"Independence is the best safeguard against this risk," he wrote. "It is also the best chance for a sustainable long-term partnership between Kosovo and Serbia."

U.N. Secretary-General Ban Ki-moon said Ahtisaari's plan "contains all of the right elements for a fair and sustainable solution to Kosovo's future status." British Foreign Minister Margaret Beckett said it "would give Kosovo clarity over its future."

U.S. Undersecretary of State Nicholas Burns said the plan would "give the Kosovars a way forward toward independence" and ensure the minority rights of the Serbs.

Kosovo's President Fatmir Sejdiu welcomed the proposal as "a historic day for Kosovo" and said that independence would serve "peace, stability and prosperity" in the province.

But Serb President Boris Tadic said he had told Burns in a telephone conversation that Belgrade was dissatisfied with the United States' support for the plan.

"Independence is unacceptable," Tadic said. "I am convinced that there is room for further negotiations. Serbia is ready for a constructive dialogue."

Ahtisaari presented his proposal to regional leaders in February. Ethnic Albanians supported the plan, while Serbian officials rejected it.

"A return of Serbian rule over Kosovo would not be acceptable to the overwhelming majority of the people of Kosovo," Ahtisaari wrote in his report to the Security Council. "Belgrade could not regain its authority without provoking violent opposition. Autonomy of Kosovo within the borders of Serbia — however notional such autonomy may be — is simply not tenable."

Ahtisaari also said that continued international administration was not sustainable.

But he also noted that Kosovo's Serb community continued to face difficult living conditions.

After the war, the Serb minority was targeted in revenge attacks and about 200,000 were forced to flee the province.

"I therefore propose that the exercise of Kosovo's independence ... be supervised and supported for an initial period by international civilian and military presences," Ahtisaari wrote. "Their powers should be strong — but focused — in critical areas such as community rights, decentralization, the protection of the Serbian Orthodox Church, and the rule of law."

Ahtisaari said some international intervention was still needed because Kosovo has a limited ability to protect minorities, develop democratic institutions and spur economic recovery and social reconciliation.

The international community's role, he said, should end only once Kosovo's authorities have implemented his settlement proposal.

In his conclusion, Ahtisaari asserted that "Kosovo is a unique case that demands a unique solution" and doesn't create a precedent for other unresolved conflicts in the world, as Russia has warned. Ahtisaari urged the council to endorse his proposal.

"Concluding this last episode in the dissolution of the former Yugoslavia will allow the region to begin a new chapter in its history — one that is based upon peace, stability and prosperity for all."