ZAGREB, Croatia (AP) _ An anti-tank mine exploded Saturday in Croatia's last Serb-held region, killing three ethnic Serbs and seriously injuring two others, Croatia's official HINA news agency reported.

U.N. spokesman Douglas Coffman said he had no details about the blast in the village of Stari Jankovci, in eastern Slavonia, Croatia's easternmost region.

The United Nations is supervising a peaceful return of Croatian rule to the region, scheduled for completion Jan. 15.

Hundreds of thousands of mines remain scattered in and around the region, remnants of the 1991 Serbo-Croat war. Teams have cleared mines from some areas, but deaths and injuries from exploding mines continue.