Tensions are again on the rise amid a new government regulation that will compel people entering Kosovo with Serbian IDs to replace them with a temporary document during their stay there.

On Sunday, ethnic Serbs in northern Kosovo — a partially recognized state bordered by Serbia in the Balkans — blocked two key border crossings with Serbia to protest the new rule.

NATO said KFOR was monitoring the situation closely “and is prepared to intervene if stability is jeopardized.”

“KFOR maintains a visible and agile posture on the ground, and the KFOR Commander is in contact with all of his main interlocutors, including the representatives of the Kosovo security organizations and the Serbian of Defense,” NATO said in a statement.