He made the remarks on Friday during a speech at a National Rifle Association (NRA) convention in Louisville, Kentucky, Xinhua news agency reported.
In his speech, Trump invoked the 2015 shooting spree at two military facilities in Tennessee, where four marines were shot down.
"We're getting rid of gun-free zones, OK," said Trump, arguing that the victims were killed because they were barred from carrying weapons and therefore could not defend themselves.
The remarks, made moments after the NRA endorsed him for president, come as the real estate tycoon-turned presidential hopeful is seeking to reconcile with Republican conservatives after a divisive primary season.
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The latest statement marked a departure from his early remarks.
In 2012, he publicly supported US President Barack Obama's call for tougher gun-safety measures in the wake of a shooting incident at Sandy Hook Elementary School in Connecticut that killed 20 children.