Kosovo police say two Serb children were wounded when a device believed to have been a hand grenade exploded on the porch of their house in the ethnically divided north.

It was the third explosion in the tense city of Mitrovica in 24 hours. The other blasts did not hurt any people.

Police spokesman Besim Hoti said a 3-year old boy and his 10-year old sister were being treated for shrapnel wounds in the Serb-run hospital in Mitrovica after the blast Monday afternoon. Their mother escaped unhurt.

The family's house borders an ethnic Albanian area, but Hoti could not say if it the incident was ethnically motivated.

Serbs in Kosovo's north largely support Serbia in its boycotting of Kosovo's 2008 declaration of independence.