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.
Serbia's president since then has accused Pristina of wanting to start a war, while his Kosovar counterpart has warned that Serbia might try to annex the predominantly Serb-populated northern part of Kosovo just as Russia annexed Crimea.
The letter to NATO from neighboring 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.
Aides said Albanian Defense Minister Mimi Kodheli and her Croatian counterpart, Damir Krsticevic, in particular wanted to focus NATO's attention on the threat to Kosovo.
The ministers told Stoltenberg that they would support transforming Kosovo's Security Force, which is lightly armed and engages in crisis response, civil protection and ordnance disposal, into a full-fledged army.
But to create such an army, Kosovo would need the support of its Serbian minority in parliament, and their representatives likely would oppose the move.
Majority ethnic Albanian Kosovo unilaterally proclaimed independence in 2008, a decade after a war with Serbian forces.
Serbia has refused to recognize the move, although Kosovo is recognized by 110 other countries. Still, until recently Serbian leaders had taken part in European Union-sponsored talks aimed at normalizing ties with Kosovo.
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.
NATO deployed peacekeepers in Kosovo after a 1999 air campaign that ousted Serbian forces fighting pro-independence ethnic Albanians. The 1998-99 conflict claimed 13,500 lives.
After receiving the letter, NATO officials said the alliance remained committed to continuing its mission in Kosovo "for as long as necessary."
At the start of its mission, NATO sent some 55,000 soldiers to Kosovo, but its contingent currently has dwindled to around 4,500.