Kosovo closed its biggest border crossing on Wednesday after protesters blocked it on the Serbian side to support their ethnic kin in Kosovo in refusing to recognise the country’s independence, Reuters reports.

With two other crossings on the Serbian border closed by similar protests on their Kosovar sides since Dec. 10, only three entry points between the two countries remain open.

The latest protest came hours after Serbia said it had put its army on the highest level of alert following weeks of escalating tensions between Belgrade and Pristina.

Serbs in Serbia used a truck and tractors on Tuesday to create the latest roadblock, close to the Merdare crossing on Kosovo’s eastern border, Belgrade-based media reported. The obstruction is preventing thousands of Kosovars who work elsewhere in Europe from returning home for holidays.

Around 50,000 Serbs living in ethnically divided northern Kosovo refuse to recognize the government in Pristina or the status of Kosovo as a country separate from Serbia. They have the support of many Serbs in Serbia and its government.