As Serbia deployed armored vehicles by a border crossing and ethnic Serbs in Kosovo protested a decision by Kosovo’s government concerning license plates, NATO forces in Kosovo have increased their patrols on the northern border near Serbia.

Serbia does not recognize Kosovo nor its license plates and has required drivers from Kosovo to remove them and purchase temporary ones while driving through Serbia.

Likewise, Kosovo opted to impose a similar measure, demanding that Serbian drivers in Kosovo pay €5 ($5.85) for a temporary license plate good in Kosovo for two months.

Ethnic Serbs in northern Kosovo reacted with fury last week, blocking roads and the two border crossings to Serbia while Serbia deployed armored vehicles and military aircraft flew over the border. The result has been the worst regional tensions in a decade.

NATO said it was “closely monitoring the situation across Kosovo” and working “to ensure a safe and secure environment and freedom of movement for all communities.” The alliance has also flown helicopters at the border over the last week to keep watch on developments.

How is the international community reacting?

The US Embassy in Belgrade, Serbia, said on Twitter that American and Canadian defense officials had visited the Jarinje and Brnjak border crossings “to gain a better understanding of the situation,” and expressed gratitude that the NATO mission known as “KFOR was on site as a stabilizing factor.”

Though the situation was calm at the border Monday, Peter Stano, the EU’s foreign affairs spokesman, said: “There are a lot of diplomatic activities going on now both in Brussels and on the ground.”

Over the weekend, the Russian ambassador to Serbia toured two military bases near the border with Nebojsa Stefanovic, the Serbian defense minister.

Like Serbia, Russia does not recognize Kosovo.

By contrast, Albanian Prime Minister Edi Rama visited Kosovo, where he criticized the “theatrical military maneuvers,” of Serbia and said the “only solution is a dialogue.”

Analysts point to the upcoming elections in both countries as a likely catalyst for the increase in tensions now.

What has Serbia’s president said?

Serbian President Aleksander Vucic has insisted that Serbia remains “committed to peace” but “won’t allow itself to be humiliated.”

In addition to military maneuvers on the border, Vucic has also vowed not to return to the negotiating table until Kosovo withdraws the forces it had sent to northern Kosovo to enforce the new license plate rules, which he has called a “criminal action.”

Vucic has also warned NATO that Serbia will intervene in Kosovo if ethnic Serbs in Kosovo come under threat.