Trump puts onus on school shooter's behavior

U.S. President Donald Trump on Thursday urged Americans to report neighbors' "erratic" behavior as he faced down calls for action after 17 people were shot dead at a Florida school. 

"So many signs that the Florida shooter was mentally disturbed, even expelled from school for bad and erratic behavior," Trump tweeted.

"Neighbors and classmates knew he was a big problem. Must always report such instances to authorities, again and again!"

This latest mass shooting - in a country where mass shootings are an almost daily occurrence - has reignited questions about America's permissive gun laws.

The suspected shooter is believed to have used a legally bought Colt AR-15, a semi-automatic weapon.

Opponents of gun control have sought to shift the debate to focus on the behavior and motives of those using the weapons.

Trump has yet to speak publicly about the shooting.