Officials say at least 13 people were killed and several were injured when a bus swayed off a bridge and plunged into a deep ravine in central Montenegro on Sunday.

Local Public Attorney Vojislav Grujic said the bus crashed some 30 kilometers north of the capital Podgorica. He said it is still unclear whether the bus is Romanian or Ukrainian.

The nationality of the passengers was not given.

Police said the bus plunged from a bridge over the Moraca river during a rain storm and crashed some 40 meters into the ravine. A helicopter was used in the rescue operation mounted by Montenegro police.