Boris Tadic was visiting Kosovo on Orthodox Good Friday
Serbian President Boris Tadic has made a rare visit to Kosovo, whose independence declaration last February was bitterly opposed by Belgrade.
The visit coincided with the deadline for parties to submit arguments to the International Court of Justice (ICJ) on the legality of Kosovo's move.
Many in Kosovo see Mr Tadic's visit as an attempt to undermine the fledgling nation, correspondents say.
Mr Tadic said he was making the visit with a "message of peace".
It was his second visit to Kosovo since it declared independence.
Authorities in Kosovo reportedly granted him permission to cross the border at the last minute.
Albanian-language daily Express said Kosovo's government had come under pressure from the US and the EU after initially refusing to let Mr Tadic enter.
The Serbian president arrived by helicopter at the 14th Century Serb Orthodox monastery of Visoki Decani, where he attended a service.
"My message today in Decani is a message of peace for Serbs, peace for Albanians, peace for all people living in Kosovo, in our Serbia," Mr Tadic was quoted as saying after lighting a candle in the church.
Major Western powers including the US backed Kosovo's declaration of independence, which has so far been recognised by 57 countries.
But Belgrade sees Kosovo as Serbian territory.
In October Serbia obtained a UN resolution calling for the ICJ to give an advisory ruling on whether Kosovo's declaration was in line with international law.
Friday is the court's deadline for the two sides to submit legal arguments and opinions in the case.