Soldiers of the Nazi-style Ustasha regime, killed during a battle in January 1943 in the town of Krasic, were thrown into the pit by the Partizans. The pit also contains the bodies of wounded people and medical staff, including nuns, who were taken from hospitals and thrown into the pit in May and June 1945, in the wake of the WWII.
So far 447 skeletons of victims have been unearthed from that site.
The commemoration at Jazovka has been organised by the Croatian Ceremonial Unit Jazovka on 22 June every year since the discovery of the pit 21 years ago, as this is the day when Croatia also marks Anti-Fascist Struggle Day as a national holiday.
According to the organiser's estimates, some 3,000 people arrived at the commemorative events at Jazovka this year.
The mass was said by Friar Nikola Barun and Idriz efendi Besic said prayers for victims of Muslim faith.
A protest letter, signed by the Croatian Ceremonial Unit's head, Boris Prebeg, was read out a calling on Croatia's authorities to help reveal "the historical truth about Croats victims of the Second World War, developments in the wake of the war and of the era of the terrorist Yugoslav Communist system".
According to the letter, there are more than 1,500 pits and multiple graves containing bodies of those victims in Croatia and an additional 600 in Slovenia.