Kosovo's president appealed for calm Saturday after seven firefighters were injured in one of two explosions that shook this ethnically divided northern city, police said.

Nato's KFOR peacekeeping force and the European Union's EULEX mission to Kosovo also reinforced their presence in the city's ethnic Albanian Bosnjacka Mahala neighbourhood where the second explosion took place, police spokesman Besim Hoti told AFP.

KFOR and EULEX issued an appeal for calm and warned that any violence would draw a stern response.

They called on "all people of Mitrovica and from all other areas of Kosovo to stay calm and to stop all violent actions".

"To any kind of threat to the safe and secure environment and the freedom of movement, KFOR and EULEX are ready to respond in a strong way," they said.

The first blast — which occurred after 10pm (2100 GMT) on Friday near a cafe in the northern half of Kosovska Mitrovica — damaged several cars but caused no injuries, Hoti said.

The second followed shortly after midnight, slightly injuring seven firefighters when an explosive device was apparently thrown at them, he said.

The firefighters were trying to put out a fire in an Albanian-owned building in Bosnjacka Mahala apparently set by a group of ethnic Serbs angered by the first explosion.

"The firefighters were wounded by bomb bursts but they are not in danger," a hospital source told AFP.

A local television journalist also sustained light head injuries, a medical source said.

Kosovo's president Fatmir Sejdiu called on the population to "avoid provocation and help law and order forces to maintain stability", while urging the incidents be investigated thoroughly.

"Such acts of violence, regardless of their authors or what their motives may be, do not contribute to the (future) of Kosovo's citizens," Sejdiu said in a statement.

Last Tuesday, a young Serb was stabbed in Kosovska Mitrovica, which is largely populated by Kosovo's minority Serbs although ethnic Albanians also live here.

His life now is out of danger, and two ethnic Albanians arrested in connection with the incident have been released after questioning.

An ethnic Albanian was also wounded in the south of the city the same day.

Kosovska Mitrovica remains deeply split and rife with tension between Serbs and ethnic Albanians, nearly a year after Kosovo — under UN administration since a 1999 Nato air war wrested control of the province from Serbia — declared independence.

More than 50 countries recognize Kosovo's independence which Serbia and Russia strongly oppose.

AFP