Below is an article published by Radio Free Europe:

NATO members Croatia and Albania are warning that Serbia poses an increasing threat to Kosovo's security as well as stability across the wider Balkans. In a joint letter this week to NATO chief Jens Stoltenberg ahead of the Munich Security Conference, the defense ministers of the two countries called on the military alliance to "revise" its peacekeeping mission in Kosovo in light of the increased threat. Tensions between Serbia and its former province Kosovo escalated after Belgrade last month sent a train painted with the slogan "Kosovo is Serbia" toward Kosovo, and Kosovo police stopped it at the border. 

The letter to NATO from neighbouring Croatia and Albania decried the "nationalistic rhetoric from Serb politicians and concrete actions on the border" that have raised tensions to be point that they threaten security and stability.

Both states are seeking to join the EU, and their integration into the bloc is seen as a way to guarantee peace in the region. But while Kosovo also seeks to join NATO, Serbian leaders have said they want to maintain ties with Russia and stay neutral.  

Another article on the same topic is published by The Guardian:

Enver Hoxhaj called on the EU, which facilitates Pristina-Belgrade talks aimed at normalising ties, to urge Serbia to remain committed to good relations an official said.

“The Republic of Kosovo encourages the European Union … to urge Serbia to remain committed to good neighbourly relations and regional cooperation and not interfere in the domestic affairs of other countries or take provocative actions which aim for the destabilisation of the region”, the minister wrote in a three-page letter. The EU foreign policy chief Federica Mogherini said she had invited the two parties to a high-level meeting of the Dialogue of Normalisation of Relations between Belgrade and Pristina next week. She tweeted: “Convening the Dialogue next Tuesday in Brussels: tensions show need for increased commitment by #Serbia and #Kosovo.