BELGRADE, Serbia

At least 12 people were killed and 31 others injured after a bus skidded off a road and overturned in northwestern Croatia on Saturday morning.

According to initial reports, the condition of 18 injured passengers is serious. All the victims are Polish citizens.

The Croatian Ministry of Interior said that police, firefighters as well as medical teams were deployed to the accident site near Varazdin, some 50 kilometers (30 miles) from the Croatian capital Zagreb.

According to reports, the bus with a Polish license plate and carrying pilgrims was traveling to Medjugorje, a Roman Catholic shrine in southern Bosnia-Herzegovina.

Investigation to determine the cause of the accident is underway.