Kosova police secure the area in front of a polling station in the ethnically divided Kosovo town of Mitrovica, where voting was marred by outbreaks of violence.
The Organization for Security and Cooperation in Europe (OSCE) has indicated that results from Kosovo's local elections on November 4 in northern Mitrovica cannot be determined because of attacks on all three polling stations there.
Kosovar election officials and OSCE monitors were evacuated from the polling stations after masked men stormed the facilities -- throwing canisters of tear gas and stealing or destroying ballot boxes.
Nikola Gaon, a spokesman for the OSCE Mission in Kosovo, told RFE/RL on November 4 that all ballots from northern Mitrovica appear to be lost.
"We don't have that material in possession and we could not hand it over [to the Central Election Commission]," he said.
Gaon doubted whether the missing ballots could ever be recovered.
"From what we have seen from the video recordings posted on YouTube and other media, that material is damaged, torn," he said. "So, in principle, I don't know where that material is -- if it ended up in trash cans or what happened to [the ballots] in the end."
Serb hard-liners had kept up their calls to boycott the vote despite Belgrade's public backing for participation by ethnic Serbs.
The OSCE's Kosovo mission chief, Jean-Claude Schlumberger, says ballots from other Serb-dominated parts of northern Kosovo were transported to a central counting station near Pristina.
Late on November 4, the Central Election Commission published preliminary results, excepting the Serb-dominated northern municipalities. They indicated there will be runoffs for the mayoral posts in most of Kosovo's 39 municipalities.
CEC President Valdete Daka said the OSCE had handed over the electoral documentation from those municipalities to election authorities, which have not yet decided whether to count the results.
Daka said officials still have to determine how many ballots were damaged during the attacks. He declined to comment on the loss of ballots from northern Mitrovica.
Kosovar President Atifete Jahjaga said the violence "will be met with a swift response" in an attempt to establish the rule of law in northern Kosovo.
In a statement, Jahjaga congratulated voters for their participation in the elections, which she said took place in "a generally calm and acceptable atmosphere."
Jahjaga added that election irregularities will be "thoroughly investigated and prosecuted by the authorities."
The U.S. Embassy in Kosovo said the international community "will not tolerate these attempts to subvert the democratic process and prevent citizens from duly electing their representatives."
Serb officials in Belgrade had called for ethnic Serbs to vote in the local elections under an EU-brokered normalization deal reached with Pristina in April.
Serbia still officially rejects Kosovo's independence, but the vote on November 4 was the first to get Belgrade's backing since Pristina's unilateral declaration of independence from Serbia in 2008.
Nevertheless, according to Washington-based political analyst Daniel Serwer, the attacks in northern Mitrovica ultimately could hurt Belgrade's bid to join the European Union.
"People in Brussels expected Belgrade to be able to do something about that," he said. "They may have tried; I don't know the answer to that question. Did they try and fail, or did they not try? I don't know. But I can tell you that it reflects badly on Belgrade and that, until they clean up the mess, they may be able to open negotiations; but those negotiations are going to have a hard time moving forward as long as this criminal element is able to escape Belgrade's control and Pristina's control."
PHOTO GALLERY: Kosovo Goes To The Polls
Scenes Of Voting In Kosovo
Many Serb voters in northern Kosovo complained about being threatened by Serb hard-liners who had called for an election boycott.
Mitrovica resident Dejana Vucmanac told reporters she was shocked by the violence.
"Today everything looks normal," she said on November 4. "But what happened yesterday was a tragedy for us. I know a lot of people who wanted to go out and vote. But they did not dare. And voting is my basic human right."
Bernd Borchardt, the head of the European Union Rule of Law (EULEX) mission in Kosovo, confirmed that EULEX police helped evacuate election monitors and workers along with ballots from parts of Kosovo that are north of Mitrovica.
"In general, I would like to underline that we are very glad that we have been able to bring the people back without major damage to health or life, and that we were able to bring the ballot boxes back because there was amazingly good turnout in the north -- 22 to 25 percent -- we've just counted this on the voters' list," he said. "So that is a good turnout."
Excluding the Serb-dominated north, voter turnout in Kosovo was about 46 percent. Turnout in parts of the north reached around 20 percent.
WATCH: RFE/RL's Kosovo Unit director Arbana Vidishiqi discusses the significance of the vote:
