"The EU condemns today’s shocking violence in #Zvecan in the strongest possible terms. The violent acts committed against @NATO_KFOR troops, media, civilians and police are absolutely unacceptable," Borrell wrote on Twitter.
He said the sides should be responsible and seek a political solution through dialogue.
"The EU urges Kosovo authorities and the protesters to immediately and unconditionally de-escalate the situation. We expect the Parties to act responsibly and find a political solution through the Dialogue immediately," Borrell said.
On Saturday, Serbia's National Security Council condemned NATO Kosovo Force (KFOR) for standing by while Kosovar police used force to install new Albanian mayors in Serb-majority northern provinces. Later in the day, Serbian Defense Minister Milos Vucevic said the Serbian army was deploying its units near Kosovo in anticipation of provocations.
On Monday, hundreds of Kosovo Serbs came to local administration buildings demanding the withdrawal of Kosovar police and officials. The KFOR mission's troops, equipped with crowd dispersal devices, were deployed in the municipalities of Zvecan, Leposaviq and Zubin Potok.
At least 52 Serbs have been injured during the clashes in Kosovo, Serbian President Aleksandar Vucic said. Media reported that at least 41 soldiers of the KFOR contingent also received injuries in clashes, with the mission itself confirming 25 injuries.