PRISTINA (Reuters) - Kosovo’s parliament ratified a 2015 border agreement with Montenegro on Wednesday after a stormy session, fulfilling a key condition for the country to gain visa-free travel to the European Union.

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The opposition Vetevendosje party had held up the vote on the deal, which they regard as a sell-out, releasing tear gas four times during the day and police arrested dozens of lawmakers.

The vote went ahead at the fifth attempt with 80 representatives voting in favour and 11 against in the 120-seat parliament.

“We have accomplished the main criteria,” parliament’s speaker Kadri Veseli said.

Prime Minister Ramush Haradinaj welcomed the vote.

“Kosovo now waits for the EU to do its part, as it was promised, so that finally Kosovo citizens can freely travel to the EU as other Europeans,” Haradinaj said in a statement.

The European Union’s top diplomat, Federica Mogherini tweeted: “Good news from Pristina: ratifying agreement on border demarcation with Montenegro, Kosovo heads towards visa free to EU for its people.”

The U.S. ambassador to Kosovo, Greg Delawie, told reporters the vote was “wonderful, wonderful news.”

Vetevendosje had been adamantly against the deal, claiming it will wrongly surrender some 8,000 hectares (30 square miles) of Kosovan territory to its neighbour.

Opposition lawmakers threw tear gas canisters into the chamber to prevent discussion and the vote, causing deputies to withdraw choking and spluttering.

The session had to be adjourned to allow the chamber to ventilate but as MPs started going back into the room, more tear gas was released, holding up proceedings again.

The EU commissioner for enlargement, Johannes Hahn, condemned the release of the tear gas in a tweet, saying: “Such behaviour has no place in a democracy.”

The EU and the United States remain the biggest supporters of Kosovo, politically and financially.

Kosovo is the only country in the Balkans whose citizens need visas to travel to EU member states. Its regional neighbours Serbia, Albania, Montenegro, Macedonia and Bosnia obtained visa-free access to Europe’s border-free Schengen zone in 2010.

Kosovo declared independence in 2008, nearly a decade after NATO air strikes drove out Serbian security forces accused of killing and expelling ethnic Albanian civilians during a counter-insurgency war.

To move towards membership of the European Union, which the government has set as its goal, Kosovo needs to soothe relations with its neighbours including Serbia which refuses to recognise Pristina institutions.