Zagreb (Croatia): 12 Polish pilgrims to Medjugorje, a Marian pilgrimage center in Bosnia and Herzegovina were killed Saturday when their bus crashed into a ditch. 31 people were injured, some critically.

Pope Francis said Sunday following his Angelus reflection that he was praying for the victims.

The accident happened at around 5:40 a.m. local time when the bus veered off the A4 road between Jarek Bisaski and Podvorec, northeast of Zagreb.

The pilgrims included three priests and six nuns, the BBC reported. The news agency said the trip to Medjugorje, the site of alleged apparitions of the Blessed Virgin Mary in Bosnia and Herzegovina, was organized by the Brotherhood of St Joseph Catholic group.

Poland's justice minister and prosecutor general ordered the Warsaw Prosecutors Office to investigate the cause of the crash, Vatican News reported.