PRISTINA (Reuters) – NATO troops stepped up patrols in Kosovo on Monday near border crossings which have been blocked by local Serbs angered by a ban on cars with Serbian licence plates entering the country in a mounting confrontation.

As the Serbian government flew overhead, video footage captured NATO’s armoured vehicles moving near the border barricades of trucks and other vehicles.

Since Monday’s number-plate ban was in effect, two major roads have been blocked by Serbs from Kosovo. This has exacerbated tensions and prompted calls from NATO and EU for calm.

All drivers coming from Serbia will now have to use temporary printed registration numbers that can be used for at least 60 days.

Kosovo claims it has reacted to Serbia’s measures against Serbian drivers who have been driving from Kosovo since Kosovo gained independence from Serbia in 2008. Serbia doesn’t recognize Kosovo’s independence, and does not have the right to register cars.

Police said that violence has already broken out in the confrontation, with two buildings belonging to the northern Kosovo interior ministry, as well as a registration office for cars, being attacked by Serbians.

Serbia began to conduct military operations near the border, and also started flying military planes over the crossing.

NATO’s mission, which has 5,000 troops in Kosovo and oversees fragile peace there, announced Monday that they had increased the frequency and duration of routine patrols in Kosovo. This included in Northern Kosovo.

After NATO bombings, Serbia took control of Kosovo in 1999.

The United States, Britain, and many EU members backed Kosovo’s declaration of independence in 2008. However, Russia is blocking Serbia from becoming a member of the United Nations.

Pristina and Belgrade agreed to engage in a dialogue with the EU to discuss outstanding issues. However, very little progress has been achieved.