Lawmakers were debating on whether to anoint Hashim Thaci, foreign minister and a former guerrilla leader, as the country's next president.
Critics say Thaci, who led the fighters of Kosovo's successful separatist war against Serbia in 1998-99, is not a unifying individual, which is what the Kosovo constitution requires. Many leading figures within the opposition are former partners of his during the war.
Thaci believes he has the votes in the 120-seat Parliament. Kosovo declared independence in 2008, although that is rejected by Serbia. Rafet Rama, a lawmaker from Thaci's Democratic Party of Kosovo, is also running for the post.
Opposition Self-Determination Movement Party leader Visar Ymeri called on supporters to join the protest to oppose Thaci's election and "until they (the government) resigns." Police have been trying to keep a small group of Thaci's supporters away from the main square. They came out despite Thaci's call to celebrate at home.
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It's not the first time that Kosovo's Parliament has faced disruption.
Since last September, the chamber has been witness to attacks involving tear gas, pepper spray, whistles and water bottles as opposition forces reject a deal between Kosovo and Serbia giving more powers to ethnic Serbs in Kosovo.
As president, Thaci would also deal with a special war crimes court created last year, which will have international judges and prosecutors to try ethnic Albanian guerrillas for the alleged killing of civilian detainees, mostly Serbs, immediately after the war ended in 1999.
Thaci was mentioned in a 2010 Council of Europe report which claimed that leaders of the now disbanded Kosovo Liberation Army were responsible for the deaths of hundreds of Serbs, Roma and ethnic Albanians suspected of collaborating with Serbs.
Thaci denies the claims.