An armed officer who stood outside a Florida school where a gunman killed 17 people last week "certainly did a poor job", the US president has said.

Deputy Scot Peterson resigned after an investigation found he failed to confront the suspect.

President Trump said the officer trained his whole life but "certainly did a poor job" protecting students.

Mr Trump said Mr Peterson was a "coward" who "didn't react properly under pressure".

"He trained his whole life but when it came time to do something he didn't have the courage," Mr Trump told reporters outside the White House on Friday. "He certainly did a poor job."

This week the president proposed arming teachers as a solution to school safety, a method that has long been championed by the powerful National Rifle Association (NRA) gun lobby.

Mr Trump touted his love for the second amendment, which protects gun rights, while speaking at the Conservative Political Action Conference (Cpac) on Friday morning.

His comments came a day after Broward County Sheriff Scott Israel revealed that Mr Peterson, the 54-year-old school resource officer, stood outside for four minutes while the alleged gunman Nikolas Cruz gunned down students at Marjory Stoneman Douglas High School.

He said video footage showed Mr Peterson arriving at the building where the shooting broke out about 90 seconds after the first shots were fired, and that he remained outside for about four minutes. The attack lasted six minutes, Sheriff Israel said.

"I am devastated. Sick to my stomach. He never went in [the school]," Sheriff Israel said.

Mr Peterson is yet to publicly comment on what happened. Officers are reportedly guarding his home.

Sheriff Israel said Mr Peterson had not given a reason for why he did not go into the building where the shooter was. It is unclear if he will face charges.

Sheriff Israel said he would not be releasing the video showing Mr Peterson and might never do so, "depending on the prosecution and criminal case" against the 19-year-old suspect accused of carrying out the shooting, former student Nikolas Cruz.

The gunman used a semi-automatic AR-15 rifle, police say, and escaped the scene before being seen and arrested later.

Read more on bbc.com.