Serbia's president has warned of potential "clashes" after neighbouring Kosovo turned back a Serbian train that bears the slogan "Kosovo is Serbia[n]".
The controversial slogan is written in 20 languages along the side of the passenger train, which is painted in the the red, blue and white of the Serbian flag and is decked out inside with religious iconography.
The train was prevent from crossing into Kosovo and returned to Belgrade over night.
"Yesterday, we were on the verge of clashes," Serbian President Tomislav Nikolic warned, following the train's return to the Serbian capital.
He accused Kosovo's leaders on Sunday of "wanting war" and warned that Serbia would defend "every inch" of its territory.
Kosovo declared independence from Serbia in 2008, but while it is supported by many in the West, Serbia does not recognise the split.
Neither does Serbia's ally Russia, setting the stage for further tensions as Kosovo's prime minister, Isa Mustafa, said he had contacted the US and the EU to express his country's concerns.
"The time of provocation, conflicts and wars should belong to the past," Mustafa said, describing the move by Serbia as "unacceptable".
Serbia contends that ethnic Serbs in Kosovo are under threat from Kosovo Albanians.
The country is officially seeking EU membership, but has also been edging more towards the Kremlin.
Serbia's Nikolic commented: "My suggestion now is only to talk in Brussels when this train is allowed to pass ... If there is no freedom of movement, what kind of Western civilization are we talking about then?"