Serbia has threatened military action against neighbouring Kosovo after its parliament approved the creation of a new army.

Kosovar MPs voted on Friday to expand the existing Kosovo Security Force into a 5,000-troop army, plus 3,000 reservists.

Belgrade called the move a “direct threat to peace and stability” in the Balkans and lashed out at the United States for supporting the proposal.

Kosovo unilaterally declared independence in 2008, but Serbia does not recognise its former province as a state.

Belgrade insists the new army would violate a UN resolution that brought to an end its bloody crackdown on ethnic Albanian separatists in 1999.

Serbian prime minister Ana Brnabic said armed intervention was “one of the options on the table”.

All 107 MPs present in the 120-seat parliament in Pristina voted in favour of passing three draft laws to expand the existing security force, created mainly for crisis response, civil defence and removal of land mines following the 1990s conflict.

Kosovo’s constitution mandates the creation of a national army but no action had been taken for years, while Pristina sought in vain to win the approval of Kosovar Serbs.

Ethnic Serb politicians in Kosovo boycotted Friday’s vote, described as “ill-timed” by Nato’s secretary general.

“I regret that this decision was made despite the concerns expressed by Nato,” said Jens Stoltenberg, warning it could destabilise a region where efforts to ease tensions have been ongoing for decades.

He added: “The North Atlantic Council will now have to re-examine the level of Nato’s engagement with the Kosovo Security Force.”

But the US called the new army “historic” and said it supported “Kosovo’s sovereign right” to maintain forces.

Birth of a nation: But will Kosovo spark another Balkan crisis? Show all 15 1 /15 Birth of a nation: But will Kosovo spark another Balkan crisis? Birth of a nation: But will Kosovo spark another Balkan crisis? An old man waves a Kosovan flag whilst Kosovo Albanians shout slogans during a rally in Pristina 2007 Getty Images Birth of a nation: But will Kosovo spark another Balkan crisis? 1389: Battle of Kosovo fought at Kosovo Polje ('Field of the Blackbirds'), in which Serbian Prince Lazar, depicted in a painting by Dura Jaksic, is killed. The comprehensive defeat by Turkish forces of the Ottoman empire was metamorphosed in folklore as a manifestation of the Serbian nation with Kosovo its cradle. Dura Jaksic Birth of a nation: But will Kosovo spark another Balkan crisis? 1974: Amidst ethnic tensions and with unrest mounting in Kosovo, Yugoslav President Tito grants the Albanian-dominated province autonomy. Reuters Birth of a nation: But will Kosovo spark another Balkan crisis? 1989: In a speech at Kosovo Polje on 28 June 1989, at the site where 600 years earlier the Serbs lost a battle against the Turks, Slobodan Milosevic restates Serbia's claim on Kosovo and outlines his new policy towards the region. With ethnic tension escalating he rescinds Kosovo's autonomy Reuters/Str Old Birth of a nation: But will Kosovo spark another Balkan crisis? 1990: A masked ethnic Albanian protesting at Kosovan independence demonstrations in Pristina, 2 February 1990. Later in the year Kosovo's Albanian leaders declare independence from Serbia, which responds by dissolving the province's government and sacking Albanian workers Reuters/Yannis Behrakis Birth of a nation: But will Kosovo spark another Balkan crisis? 1998: During fighting in Kosovo, 9 June 1998, ethnic Albanian refugees, led by an armed Kosovo Liberation Army (KLA) fighter, escape to Albanian soil. A Serbian crackdown on the separatist KLA leads to increased fighting with hundreds of thousands of Albanians Kosovans beginning to flee across the border. This prompts a warning about their treatment from Nato to president Milosevic Reuters/Yannis Behrakis Birth of a nation: But will Kosovo spark another Balkan crisis? 1999: A Serbian man surveys his destroyed home after Nato bombings hit the town of Aleksinac, 124 miles south of Belgrade, 6 April 1999. Following continued Nato air strikes against Yugoslavia, president Milosevic finally withdraws troops from Kosovo. Nato soldiers arrive in support of UN administration Yugoslav Army/RL/Getty Images Birth of a nation: But will Kosovo spark another Balkan crisis? 2002: Kosovan parliamentary elections take place and Albanian parties share power. Ibrahim Rugova (left) of the Democratic League of Kosovo and Bajram Rexhepi (right) from the Democratic Party of Kosovo are elected president and prime minister respectively, 4 March 2002 Reuters/Hazir Reka Birth of a nation: But will Kosovo spark another Balkan crisis? 2005: The debris following a roadside bomb in Kosovo's capital, Pristina, intended to assassinate president Ibrahim Rugova, 15 March 2005. He survives the attack but another explosion goes off near the Kosovan parliament and unrest continues Nikola Besevica/AFP/Getty Images Birth of a nation: But will Kosovo spark another Balkan crisis? 2006: Thousands line the streets of Pristina for the funeral of president Ibrahim Rugova, who died from lung cancer, 21 Janurary 2006. He is replaced as president by Fatmir Sejdiu. UN-sponsored peace talks begin between ethnic Serbian and Kosovan leaders. Tension continues as Serbia approves new constitution declaring Kosovo a part of the country Dimitar Dilkoff/AFP/Getty Images Birth of a nation: But will Kosovo spark another Balkan crisis? 2007: Russia blocks internationally-agreed peace plan for 'supervised independence' in UN security council. Troika of international mediators given one last chance to find negotiated solution by 10 December. They fail. Hashim Thaci, a former KLA leader, wins general election in Kosovo in November and becomes prime minister-elect. His party, the Democratic Party of Kosovo favours speedy independence but Thaci is persuaded to delay any such declaration in cooperation with the US and EU Dimitar Dilkoff/AFP/Getty Images Birth of a nation: But will Kosovo spark another Balkan crisis? 2008: A board which reads, 'Independence', at the entrance of Pristina, 15 February 2008. Prime minister Hashim Thaci is poised to confirm on 17 February as the day Kosovo will declare independence from Serbia. It will do so with strong support from the major EU powers and the United States, and equally vigorous opposition from Serbia and Russia, which have vowed never to recognise it Dimitar Dilkoff/AFP/Getty Images) Birth of a nation: But will Kosovo spark another Balkan crisis? 2008: 'Fireworks exploded. Horns sounded. And the nation of Kosovo was created.' Kosovars celebrate in the centre Pristina following the declaration of independence by Kosovo's parliament, 17 February 2008 Daniel Mihailescu/AFP/Getty Images Birth of a nation: But will Kosovo spark another Balkan crisis? 2008: Kosovo's president Fatmir Sejdiu (l) and prime minister Hashim Thaci (r) wave to crowds during independence celebrations in Pristina, 17 February 2008 Dimitar Dilkoff/AFP/Getty Images Birth of a nation: But will Kosovo spark another Balkan crisis? 2008: Serbian youths clash with police in Belgrade during a protest against Kosovo's independence declaration, 17 February 2008. Rioters targetted the embassies of countries backing Kosovo's independence STR/AFP/Getty Images

Kosovo’s prime minister Ramush Haradinaj said the new army “will never be used against” Serbia.

He added: “Serbia’s army will now have a partner – Kosovo’s army – in the partnership for peace process.”

But Belgrade fears the army could be used to chase the Serbs out of Kosovo’s north, a claim strongly denied by the government in Pristina.

On Friday, Nikola Selakovic, an adviser to the Serbian president, said his country could send in troops or declare Kosovo an occupied territory. Belgrade’s foreign minister Ivica Dacic said Serbia would seek an urgent session of the UN Security Council about the issue.

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President Aleksandar Vucic who visited his country’s troops near the border with Kosovo on Friday, later addressed the nation, denouncing the US for its apparent support of a Kosovar army and praising allies Russia and China for their opposition to the move.

He claimed Kosovo and its “sponsor” – the US – wanted to “quash” the Serbs.

Mr Vucic said Serbia had been “brought to the edge” by Kosovo’s decision and now had no choice but to “defend” itself.

Antonio Guterres, UN secretary general, called on “all parties concerned to exercise restraint and refrain from actions that could raise tensions”.

Any Serbian armed intervention in Kosovo would mean a direct confrontation with thousands of Nato-led peacekeepers, including US soldiers, who have been stationed in Kosovo since 1999.