A low-key ceremony marked the signing of the constitution
A new constitution has come into force in Kosovo - handing power to the majority ethnic Albanian government after nine years of UN rule.
It comes four months after Kosovo declared independence from Serbia in a move backed by the West but opposed by Serbia and its ally, Russia.
An EU mission is being deployed in a supervisory role, but Russia has blocked a formal handover from the UN.
Serbia says the constitution will not apply in Serb-dominated north Kosovo.
In a low-key ceremony in the Kosovan capital Pristina, Kosovo President Fatmir Sejdiu signed a package of laws, creating Kosovo's first ministry of defence, army and foreign ministry.
This is something which previously only the United Nations had the power to do.
It remains unclear who will oversee Kosovo's Serb-run areas
Serbian President Boris Tadic has warned that the constitution would have harmful consequences.
"Serbia does not accept the proclamation of Kosovo's constitution as a legal fact," he said.
In the divided city of Mitrovica, the minister for Kosovo in the outgoing Serbian government, Slobodan Samardzic, announced the establishment of a new Serbian parliament in Kosovo, made up of Serb representatives elected in Serbian elections in May.
Security is high in Mitrovica after a gunman attacked a police station on Saturday.
The unidentified attacker was wounded along with a policeman in the incident, police said. It was not immediately clear in which part of the town the shooting took place.
UN role unclear
Under the new constitution, which came into force at midnight on Sunday, Kosovo's government assumes many of the powers held up until now by the UN.
"The will of the people of Kosovo and [the] Ahtisaari plan are included in the constitution," Kosovo's Deputy Prime Minister Hajredin Kuci told the AP Television.
Mr Kuci was referring to the plan drawn up by former UN envoy Martti Ahtisaari, which envisaged the decentralisation of Kosovo and considerable autonomy for Kosovo Serbs.
The plan - backed by Western countries - has not been formally approved, due to Russian objections.
The EU is to deploy several missions to the territory, including a 2,200-strong Law and Justice Mission (Eulex).
The Eulex had been due to start its work over the weekend, but Russia - a staunch Serbian ally - has blocked the handover, saying the move has not been approved by the UN Security Council.
On Thursday, UN Secretary General Ban Ki-moon set out plans to start ceding UN functions in Kosovo to the EU, despite Russian objections.
The majority ethnic Albanian authorities are now in charge of Kosovo, according to the constitution.
"It is my intention to reconfigure the structure and profile of the international civil presence to one that... enables the European Union to assume an enhanced operational role in Kosovo," Mr Ban said.
Serbia said Mr Ban had no authority to reconfigure the UN mission.
It is unclear on whether the row will mean the UN will not withdraw.
But Pieter Feith, the EU's special representative in Kosovo, said the UN thought it was the right time to hand over power to the Kosovo government.
"We think this is a significant new period that is starting," he said.
"The secretary general of the United Nations has recognised realities on the ground and has decided to reconfigure the United Nations presence here and this will give the government full authority in all its competencies."
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