Palestinian gunmen and security forces exchanged fire before dawn Saturday in Gaza but no one was injured, witnesses and security officials said. The shootout began when at least 40 gunmen from various Palestinian groups attacked a security headquarters in the city. Shooting continued intermittently for three hours, The Associated Press reported. Soon after the fighting stopped shots were fired near the Gaza house of a Palestinian security chief, Brig. Gen. Rashid Abu Shbak, but no injuries were reported.