In September 1991, Croatian National Guard (ZNG) organised armed incursions across the Croatian border into Bosnia. ZNG opened mortar fire on Bosanska Dubica on 13 September 1991, and raided Bosanski Brod on 15 September 1991.
On 20 September 1991, the JNA transferred troops to the front at Vukovar via the Višegrad region of northeastern Bosnia. In response, local Croats and Bosniaks set up barricades and machine-gun posts. They halted a column of 60 JNA tanks but were dispersed by force the following day. More than 1,000 people had to flee the area. This action, nearly seven months before the start of the Bosnian War, caused the first casualties of the Yugoslav Wars in Bosnia.