"He's an emblematic figure, after Rugova perhaps the best-known figure in the LDK. He was in the party from the beginning," said an LDK supporter, who asked not to be named.
An eyewitness told Reuters news agency that Xhemajl Mustafa was shot as he and another person walked up the stairs at the entrance to his block of flats in the Dardania district.
Earlier, Nato peacekeeping forces closed a border road between Kosovo and an area of Serbia allegedly controlled by Albanian separatists, in response to clashes with Serbian police earlier in the week.
Witnesses to the Pristina shooting said that a crowd gathered in the street following the shooting, which took place in a densely populated area of the city packed with bars, cafes and high-rise blocks of flats.
K-For troops sealed off the area while police began their investigation.
Key figure
Mr Mustafa was a leading member of Mr Rugova's moderate nationalist Democratic League of Kosovo (LDK) and one of the veteran pacifist's closest political aides.
"He's an emblematic figure, after Rugova perhaps the best-known
figure in the LDK. He was in the party from the beginning," said an LDK supporter, who asked not to be named.
The LDK won a landslide victory in municipal elections on 28 October, provoking fears of a backlash from hardline elements in rival parties which sprang from the Kosovo Albanian guerrilla movement, the Kosovo Liberation Army.
Border attacks
Earlier on Thursday, United States peacekeepers from the Nato-led force closed a border road from Kosovo to the village of Dobrosin in southern Serbia.
The village is believed to be a base for Albanian rebels responsible for carrying out attacks on Serbian police over the last few days.
Serbian authorities later said a group of armed Kosovo Albanians also blocked a road leading from the southern town of Bujanovac to Kosovo.
Four Serbian policemen were found dead on Wednesday in a border security zone in southern Serbia after clashes with suspected guerrillas.
And K-For troops arrested 10 suspected guerrillas in the border area between Kosovo and Serbian-controlled territory.
K-For also seized a lorry carrying grenades, mortar rounds, landmines and other weapons in a separate operation in the same area.
The incidents have occurred amid increasing frustration among many Albanians over their hopes for independence for Kosovo.
Yugoslavia's integration with the international community following the election of President Vojislav Kostunica has been interpreted by many as standing in the way of Kosovo Albanians' plans for statehood.