Hundreds of ethnic Serbs in the north of Kosovo have prevented Nato peacekeepers from removing barricades which have blocked off the area for the past three months.
Troops in riot gear tried to push through three of the 16 roadblocks overnight, but were met by protesters who sat on the roads to stop the advance.
The Serbs say they are preventing the Albanian-majority government in Kosovo from sending any officials into the Serb-dominated north.
However, Nato says it must have unimpeded access to the area.
The barriers were erected in July when the mainly ethnic Albanian government sought to take control of crossing points at Jarinje and Brnjak to enforce a trade blockade against Serbia.
The ban was imposed in response to Serbia's effective bar on imports from Kosovo since the territory declared independence in 2008.
But in the Serb-dominated north of Kosovo, many feared the move to put Kosovo Albanian customs and police officials on the border would severely limit their access to Serbia.
"As long as KFOR [Nato peacekeeping force] tries to deploy Kosovo authorities in the north of Kosovo by force, freedom of movement is impossible," said Kosovo Serb official Slavisa Ristic, according to the Associated Press news agency.
The barricades are formed from vehicles, rocks, mud and logs.
On Friday, the commander of Nato-led peacekeepers Maj Gen Erhard Drews warned force would have to be used if the action persisted.
About 40,000 Serbs live in northern Kosovo, making up the majority in a number of towns. They refuse to recognise the authority of the predominantly ethnic Albanian government in Pristina.
The unilateral declaration of independence has been recognised by around 80 countries, despite strong opposition from Belgrade.
A greater number of countries have withheld recognition.