Kostunica visited the Serbian monastery at Gracanica, where he attended a religious commemoration. He told Serbs gathered there that Serbia "wants compromise," but that "Kosovo has been and always will be part be part of Serbia."
Police arrested about 120 ethnic Albanians protesting Kostunica's visit, which comes during UN-brokered talks on the future of the UN-administered province.
In 1389, the Serbs were defeated in the Battle of Kosovo Polje, leading to more than 500 years of Ottoman domination. Despite the defeat, the battle has become a key symbol of Serbian nationalism for many Serbs.
Kostunica missed a commemoration at the site of the medieval battle amid security fears.