PRISTINA (Reuters) - The head of NATO urged the leaders of Kosovo and Serbia on Friday to ease the tension that has grown in recent weeks since Serbia sent a train painted with the slogan “Kosovo is Serbia” to the border and Kosovo police stopped it entering.

Serbia’s president has accused the authorities in Pristina of wanting to start a war, while his Kosovo counterpart has said Serbia could use the model of Russia in Crimea to annex the northern part of Kosovo.

Tensions rose further this week when the Kosovo authorities said they would remove a wall in the ethnically divided town of Mitrovica built by Serbs there.

“Not more rhetoric but we need dialogue, we need to reduce tensions to avoid incidents...and move forward normalizing the process between Pristina and Belgrade,” NATO Secretary General Jens Stoltenberg told reporters after meeting Kosovo Prime Minister Isa Mustafa.

The integration of the Western Balkan countries into the EU and NATO is seen by the two institutions as a way to guarantee peace in a region still scarred by the wars that followed the collapse of Yugoslavia in the early 1990s.

Kosovo, backed by the U.S. and major western European states, declared independence from Serbia in 2008. Belgrade considers it part of its territory and supports the Serb minority there.

NATO still has around 4,500 troops stationed in Kosovo to keep the fragile peace.

Kosovo Albanians make up more than 90 percent of Kosovo’s 1.8 million population. Northern Kosovo is home to a Serb minority of around 40,000 to 50,000 people who do not consider Pristina their capital.

Normalizing relations between Kosovo and Serbia is a key condition for both countries to progress in their bids to join the European Union.