During the Bosnian War, there was an ethnic cleansing campaign committed by the Bosnian Serb political and military leadership – Army of the Republika Srpska, mostly against Bosniak and Croat civilians in the Prijedor region of Bosnia and Herzegovina in 1992 and 1993. The composition of non-Serbs was drastically reduced: out of a population of 50,000 Bosniaks and 6,000 Croats, only some 6,000 Bosniaks and 3,000 Croats remained in the municipality by the end of the war. Apart from the Srebrenica massacre, Prijedor is the area with the highest rate of civilian killings committed during the Bosnian War. According to the Sarajevo-based Research and Documentation Center (IDC), 4,868 people were killed or went missing in the Prijedor municipality during the war. Among them were 3,515 Bosniak civilians, 186 Croat civilians and 78 Serb civilians. As of October 2013^[update], 96 mass graves have been located and around 2,100 victims have been identified, largely by DNA analysis.

The International Criminal Tribunal for the Former Yugoslavia (ICTY) sentenced 20 people in relation to crimes perpetrated in Prijedor, finding them guilty of persecutions on political, racial or religious grounds; murder; inhumane acts; extermination; deportation or forced displacement (crimes against humanity), and wanton destruction of cities, towns or villages or devastation not justified by military necessity; destruction or wilful damage done to institutions dedicated to religion (violations of the laws or customs of war).

The crimes committed in Prijedor have been subjected to 13 trials before the International Criminal Tribunal for the Former Yugoslavia. Politicians, soldiers and police officers in the Serb SDS and crisis staff, including Milomir Stakić, Milan Kovačević, Radoslav Brđanin, ranging to the highest leaders including general Ratko Mladić, Bosnian Serb president Radovan Karadžić, and Serbian president Slobodan Milošević have been charged with genocide, persecution, deportation, extermination, murder, forced transfers, and unlawful confinement, torture as crimes against humanity (widespread, systematic attacks against a civilian population) and other crimes, have been alleged to have occurred in Prijedor. The ICTY has characterized the Prijedor events of 1992 as having met the "actus reus" (guilty act) of genocide through killing members of the group and causing serious bodily and mental harm to members of the group. However, the requirement of the specific intent to physically destroy was not established beyond reasonable doubt. However, the events of 1992 in Prijedor were part of the larger joint criminal enterprise to forcibly remove Bosnian Muslims and Croats from large territories of Bosnia. In 2013, investigators were led by two Bosnian Serb civilians who worked in and around the camps to a mining complex Ljubija, unearthing the largest mass grave in Bosnian war, and the discovery of over 1,000 bodies in both the Tomašica and Jakarina Kosa mine mass grave sites.

Following Slovenia's and Croatia's declarations of independence in June 1991, the situation in the Prijedor municipality rapidly deteriorated. During the war in Croatia, the tension increased between the Serbs and the communities of Bosniaks and Croats.

Bosniaks and Croats began to leave the municipality because of a growing sense of insecurity and fear caused by intensifying Serb propaganda. The municipal newspaper Kozarski Vjesnik started publishing allegations against the non-Serbs. The Serb media propagandised the idea that the Serbs had to arm themselves. Terms like Ustasha (Ustaše), Mujahideen (Mudžahedini) and Green Berets (Zelene beretke) were used widely in the press as synonyms for the non-Serb population. Radio Prijedor disseminated propaganda insulting Croats and Bosnian Muslims. As one result of the takeover of the transmitter station on Mount Kozara in August 1991 by the Serbian paramilitary unit the Wolves of Vučjak, TV Sarajevo was cut off. It was replaced by broadcasts from Belgrade and Banja Luka with interviews of radical Serb politicians and renditions of Serb nationalist songs, which would previously have been banned.

On 7 January 1992, the Serb members of the Prijedor Municipal Assembly and the presidents of the local Municipal Boards of the Serbian Democratic Party proclaimed the Assembly of the Serbian People of the Municipality of Prijedor and implemented secret instructions that were issued earlier on 19 December 1991. The "Organisation and Activity of Organs of the Serbian People in Bosnia and Herzegovina in Extraordinary Circumstances" provided a plan for the SDS take-over of municipalities in BiH, it also included plans for the creation of Crisis Staffs. Milomir Stakić, later convicted by ICTY of mass crimes against humanity against Bosniak and Croat civilians, was elected President of this Assembly. Ten days later, on 17 January 1992, the Assembly endorsed joining the Serbian territories of the Municipality of Prijedor to the Autonomous Region of Bosnian Krajina in order to implement creation of a separate Serbian state on ethnic Serbian territories.

On 23 April 1992, the Serbian Democratic Party decided inter alia that all Serb units immediately start working on the takeover of the municipality in co-ordination with the Yugoslav People's Army and units of the future Army of the Republika Srpska). By the end of April 1992, a number of clandestine Serb police stations were created in the municipality and more than 1,500 armed Serbs were ready to take part in the takeover.

A declaration on the takeover prepared by the Serb politicians from the Serbian Democratic Party was read out on Radio Prijedor the day after the takeover and was repeated throughout the day. When planning the anticipated takeover, it was decided that the 400 Serb policemen who would be involved in the takeover would be sufficient for the task. The objective of the takeover was to take over the functions of the president of the municipality, the vice-president of the municipality, the director of the post office, the chief of the police etc.