The spokeswoman for the UN mission in Kosovo, Clarisse Pasztory, said that the UN administration decided in consultation with the KFOR international peacekeeping force to allow Kostunica to visit Kosovo privately for religious reasons.
KFOR spokesman Colonel Yves Kermorvan said that KFOR troops had taken only routine security measures for the visit.
Kostunica is the first prime minister of Serbia to have visited the southern province since the 1999 war.
The liturgy was led by the Patriarch of the Serbian Orthodox Church, Pavle, who called for peace between the Serb minority and the ethnic Albanian majority.