A sheriff in Florida says he will not resign amid mounting criticism for the armed officer who failed to act during the massacre at a high school in Parkland, saying the deputy's response was "not [his] responsibility".

Scott Israel, the Broward County Sheriff, insisted only one of his armed deputies is so far known to have been at fault for staying outside the school during the attack rather than entering to confront the gunman. Nikolas Cruz, a 19-year-old former student at the school, has been charged with the killings.

In the wake of the shooting, Donald Trump called for teachers to be armed, saying “gun-adept” teachers, coaches, and other school workers would be able to deter school shooters.

But it later emerged that there had been an armed policeman, identified as the school's resource officer Scot Peterson, was nearby when the shooting began but did not go into the building.

Florida shooting – in pictures Show all 10 1 /10 Florida shooting – in pictures Florida shooting – in pictures Police arrest a suspect in connection with the shooting at the Marjory Stoneman Douglas High School in Parkland, Florida Reuters Florida shooting – in pictures Parents wait for news after reports of a shooting at Marjory Stoneman Douglas High School in Parkland, Florida AP Florida shooting – in pictures Anxious family members wait for news of students AP Photo/Wilfredo Lee Florida shooting – in pictures Students being evacuated from the school AP Florida shooting – in pictures Students being evacuated from the school Getty Florida shooting – in pictures People gather waiting for word from students AP Florida shooting – in pictures Parents waiting for news on their children AP Florida shooting – in pictures People gather at a hotel where students were taken after the shooting Getty Florida shooting – in pictures Florida Governor Rick Scott speaks to the media as he visits Marjory Stoneman Douglas High School following the shooting AFP/Getty Florida shooting – in pictures Dr. Igor Nichiporenko, Medical Director Trauma, left, and Dr. Evan Boyer, Medical Director, Emergency Services, speak about treating victims and the suspect at a press conference outside Broward Health North hospital AP

Mr Peterson has resigned rather than face suspension and possible dismissal.

“Leaders are responsible for the agency, but leaders are not responsible for a person,” Mr Israel said in an interview with NBC.

“I gave him a gun. I gave him a badge. I gave him the training. If he didn’t have the heart to go in, that’s not my responsibility.”

The sheriff’s office is also facing a backlash for allegedly mishandling 18 tip-off calls concerning the suspected shooter.

Various news outlets, including CNN and NBC, have since reported at least three more armed Broward County sheriff’s deputies were present on the scene of the shooting, taking cover behind their vehicles instead of immediately going into the school.

Mr Israel dismissed the reports as “absolutely untrue”.

“Our investigation to this point shows that during this horrific attack, while this killer was inside the school, there was only one law enforcement person, period, and that was former deputy Scot Peterson,” he said in an interview with CNN.

However, he did not rule out that the investigation could find other deputies who failed to act properly during or immediately after the shooting, which authorities said lasted for six or seven minutes.

He rejected calls for his removal as politically motivated and defended his department from the criticism his deputies overlooked a number of allegations that Mr Cruz posed a threat of violence.

Parents and students walk by the memorial for the victims of the shooting at Marjory Stoneman Douglas High School as they returned to the school for the first time since the tragedy (David Santiago/Miami Herald via AP)

“I can only take responsibility for what I knew about,” Mr Israel told CNN, adding he had “given amazing leadership” since he was first elected sheriff in 2012.

Aside from Mr Peterson’s resignation, Mr Israel previously said two other deputies were placed on restricted duty, pending an internal review of whether they handled two tips, from 2016 and 2017, warning Mr Cruz was collecting weapons and could commit a school shooting.

He told CNN 16 other “calls for service” his department received about Mr Cruz before the massacre were properly handled, though others disagreed.

Signs calling for gun legislation left during a march at the US Courthouse in Fort Lauderdale, Florida (REUTERS/Joe Skipper) (Reuters)

On Sunday, 74 Republican members of the Florida House of Representatives urged Rick Scott, the state’s Governor, to suspend Mr Israel.

“In the years leading up to this unspeakable tragedy, Sheriff Israel, his deputies and staff ignored repeated warning signs about the violent, erratic, threatening and antisocial behaviour” of the accused gunman, the letter said. It cited additional questions raised about the actions of the first deputies on the scene of the shooting.

The FBI has also drawn public outrage by acknowledging it failed to follow proper protocols after receiving a tip saying Mr Cruz possessed a gun, had indicated the desire to kill and could carry out a school shooting.