US President Donald Trump has claimed he would not have hesitated to storm the Florida high school where 17 people were shot dead, even if he unarmed.

The President’s assertion comes as an armed officer, heavily criticised for failing to enter the besieged school during the massacre, has broken his silence on his actions.

“You don’t know until you test it, but I think, I really believe I’d run in there, even if I didn’t have a weapon,” Mr Trump told a gathering of US governors at the White House on Tuesday morning (AEDT).

“And I think most of the people in this room would have done that too.”

Mr Trump lambasted the inaction of sheriff’s deputies, who are accused of failing to take on the Marjory Stoneman Douglas High School shooter, saying they “weren’t exactly Medal of Honour winners”.

He signalled more than one officer was fault and said that their performance was “frankly disgusting”.

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“The way they performed was really a disgrace,” he added.

The President also attacked Scot Peterson, a veteran officer who had been assigned to the school but remained outside as the shooting unfolded.

He said the armed school resource officer “choked”, following comments last week when he said Mr Peterson “didn’t have the courage”.

Mr Trump’s comments came as Mr Peterson’s lawyer issued his first public statement about the attack, saying it was “patently untrue” that the deputy failed to meet sheriff’s department standards or acted with cowardice.

Mr Peterson resigned after Broward County Sheriff Scott Israel said he felt sick to his stomach over his deputy’s failure to intervene.

“Let there be no mistake, Mr Peterson wishes that he could have prevented the untimely passing of the 17 victims on that day, and his heart goes out to the families of the victims in their time of need,” attorney Joseph DiRuzzo said in the statement.

The sheriff’s account of Peterson’s actions that day was a “gross oversimplification” of the events, Mr DiRuzzo said.

Mr Trump stressed a the need for action in the wake of the Florida school shooting, telling governors the only way to stop school shootings was “retribution”.

“You’re not going to stop it by being kind.”

Mr Trump defended his proposal of arming and training some school teachers to use firearms, saying he only wanted “highly trained people that have a natural talent [for shooting], like hitting a baseball, or hitting a golf ball, or putting” to handle weapons in schools.

He compared the skill required to play golf with handling a firearm, where “some people always make the 4-footer, and some people under pressure can’t even take their club back”.

Mr Trump also told governors not to worry about the National Rifle Association lobbying group as states consider how to improve school safety.

“Don’t worry about the NRA. They’re on our side,” he said.

“And you know what, if they’re not with you, we have to fight them every once in a while. That’s OK. They’re doing what they think is right.”

The massacre was the second-deadliest ever shooting at a US school.

Mr Trump’s comments were in stark contrast to those made by his wife Melania, who told the governor’s spouses she supported the stance taken by Marjory Stoneman survivors who are pushing for gun reform.

“I have been heartened to see children across this country using their voices to speak out and try to create change. They are our future and they deserve a voice,” Mrs Trump said.

-with AAP