The NATO-led KFOR peacekeeping force in Kosovo has stepped up patrols on the border with Serbia amid worsening tensions between the two Balkan countries over a dispute about license plates.
"KFOR has increased the number and time length of the routine patrolling all around Kosovo," including in the mainly Serb northern part of the country, the force said in a statement on September 27.
Video footage showed NATO armored vehicles moving close to the barricades made of trucks and other vehicles on the Kosovo-Serbia frontier, as Serbian government jets flew overheard.
The U.S. Embassy in Serbia tweeted that U.S. and Canadian defense officials had visited the Jarinje and Brnjak border crossings "to gain a better understanding of the situation."
"They were glad to note KFOR was on site as a stabilizing factor," the embassy said.
The two border crossings have been blocked by local Serbs since Kosovar authorities on September 20 required all drivers from Serbia entering Kosovo to use temporary printed registration details that are valid for 60 days.
The Kosovar government says it is in retaliation for measures in force in Serbia against drivers from Kosovo since 2008, when Kosovo declared independence from Serbia. Belgrade does not recognize Kosovo's independence and therefore its right to take official actions such as registering cars.
WATCH: Albanian PM Urges Serbia To End 'Show Of Force' Near Kosovo Border
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Albanian PM Urges Serbia To End 'Show Of Force' Near Kosovo Border
The move to increase KFOR patrols comes a day after Serbian President Aleksandar Vucic warned NATO that Serbia will intervene in Kosovo if Serbs there come under serious threat from the majority Kosovar Albanians.
The confrontation has already boiled over into violence, with a car registration office and another Interior Ministry buildings in northern Kosovo being attacked on September 25, according to police.
Serbia has also begun military maneuvers near the border and started flying military jets above the crossings in protest.
NATO has led KFOR since 1999, with around 4,000 troops from 28 countries, after a 78-day bombing campaign by the military alliance ended the 1998-99 Kosovo War that left more than 10,000 dead.
KFOR is supported by the United Nations, the European Union, and other international actors. Its aim is to stave off lingering ethnic tensions between Kosovo's Albanian majority and Serbian minority.
Kosovo's declaration of independence is backed by the United States, Britain, and most EU member states, but its membership of the United Nations is blocked by Russia, Serbia's traditional ally.
Belgrade and Pristina committed to an EU-sponsored dialogue in 2013 to resolve outstanding issues, but little progress has been made.
On September 27, Kosovar Prime Minister Albin Kurti repeated an offer for both countries to lift the rule of temporary license plates. He also said they were open to talks in Brussels, but Belgrade was declining to hold them.
Vucic has described Kosovo's recent license-plate move as a "criminal action," and he made the withdrawal of all Kosovar special police a condition of EU-mediated negotiations to resolve the dispute.
On September 26, Serbian Defense Minister Nebojsa Stefanovic visited troops at two military bases near the Kosovo border, accompanied by Russia's ambassador to Serbia.
The EU, NATO, and the United States have all urged Kosovo and Serbia to immediately exercise restraint and refrain from unilateral actions.
European Commission spokeswoman Diana Spinant on September 27 urged both sides to "sit down together and to put an end to the verbal escalation in the region."
The European Union hopes Serbian and Kosovar negotiators will meet, said the bloc's spokesman on foreign affairs, Peter Stano.
"There are a lot of diplomatic activities going on now both in Brussels and on the ground," Stano told reporters.
Albanian Prime Minister Edi Rama on September 27 visited Kosovo and criticized Serbia's "theatrical military maneuvers," saying that the "only solution is a dialogue.”