EU Foreign Policy Chief Josep Borrell called for calm on Monday amid violence across Kosovo’s ethnic Serbian north. Recent political flashpoints have reignited decades of tensions between minority Serbs and majority Kosovo Albanians. Borrell ordered, “[b]arricades must be removed immediately by groups of Kosovo Serbs. Calm must be restored.” He also demanded that all parties “avoid escalation.”

Tensions increased after Kosovo’s Assembly voted in January to ban the country’s Serbs from voting in Serbia’s constitutional referendum. The ban passed unanimously, and lawmakers expressed a need to reaffirm the country’s electoral sovereignty.

More recently, Kosovo passed a measure to phase out Serbian-issued license plates. The measure mandates fines and allows authorities to confiscate vehicles for non-compliance. The US strongly encouraged Kosovo to extend the law’s implementation period “in the interest of making progress on the EU-facilitated dialogue to normalize Kosovo-Serbia relations.” However, the plan went into effect on November 1.

An ethnic Serbian police officer was dismissed soon after for refusing to issue the required fines. In response to his dismissal, hundreds of additional ethically Serbian police officers and lawmakers resigned. The mass resignation forced both Kosovo and Serbia to negotiate an EU-facilitated compromise; with an agreement announced at the end of November.

However, de-escalation was short-lived. On Saturday, an ethnic Serbian police officer who resigned in November was arrested and held on suspected terrorism. The arrest prompted the erection of road blocks and an exchange of gunfire between Kosovo Police Force (KPF) and unknown assailants. Kosovo’s prime minister, Albin Kurti, has asked NATO’s Kosovo Force (KFOR) to address the situation and restore order. Additionally, Serbian president Aleksandar Vucic announced Serbia will ask KFOR’s permission to send its own troops into Kosovo.

Serbia and Kosovo fought a bitter civil war in 1998 and 1999. Although Kosovo declared independence from Serbia in 2008, Serbia has never recognized the sovereignty of Kosovo. NATO maintains around 4,000 peacekeepers and support staff in Kosovo.