Complex sentence: The fighting erupted despite a ceasefire arranged days ahead and led JNA General Veljko Kadijević to pull out from negotiations regarding implementation of the ceasefire details and issue an ultimatum to Croatian authorities against capture of further JNA facilities.
Split into simpler sentences: The fighting erupted despite a ceasefire that had been arranged days before, and caused JNA General Veljko Kadijević to withdraw from negotiations regarding the ceasefire's implementation. He subsequently issued an ultimatum to Croatian authorities, warning against the capture of further JNA facilities.