"Adopting the constitution represents the second historic moment for Kosovo after the proclamation of independence [from Serbia on February 17]."
Some 40 countries have recognised Kosovo's ethnic-Albanian majority declaring independence. Serbia rejects its secession and wants more negotiations on its status.
"Serbia does not accept the proclamation of Kosovo's constitution as a legal fact," Boris Tadic, the Serbian president said.
"Serbia regards Kosovo as its own southern province, and is defending its integrity by peaceful means, through diplomacy, not force."
Tadic also said the new charter was "a political event with ... harmful consequences".
Pieter Feith, the international civilian representative for Kosovo, told Al Jazeera that Serbian co-operation is vital.
"I think what could help is a government in Belgrade with a pro-European outlook, and would recognise that the best way to bring stability to this region is for Kosovo to become a multi-ethnic state," he said.UN 'reconfiguration'
The implementation of the constitution now paves the way for the country to take over from a nine-year-old UN mission in the country.
|The UN presence in Kosovo may|
remain in place for many months to come
However, a formal handover of the UN to the government in Pristina has not yet occurred.
This is attributed to a Russian veto of a proposal, suggested by Ban Ki-moon, the UN secretary-general, regarding a so-called "reconfiguration" of the world body's presence in the country.
This involves the deployment of Eulex, a 2,000-strong EU police and justice mission. Eulex is meant to operate alongside Nato's 16,500 peacekeeping troops.
The constitution, unanimously approved by Kosovo's parliament, paves the way for the introduction of Eulex.
The new arrangement is based on a blueprint for Kosovo's "supervised independence" put forth by Martti Ahtisaari, a UN special envoy, after status talks between Kosovo Albanian and Serbian leaders collapsed at the end of 2006.
Ban informed Sejdiu and Tadic of his plans to restructure Unmik, the UN mission in Kosovo, by transferring many of its powers to local institutions and the EU.
Unmik has run Kosovo since 1999, when Nato forces took control after ousting forces loyal to the late Serbian president Slobodan Milosevic.
Russia, a traditional ally of Serbia, blocked approval of the plan before the UN Security Council where it is a veto-wielding permanent member.
Moscow insists the 27-member EU bloc has no mandate to go forward with the plan.