Students react following a shooting at Marjory Stoneman Douglas High School in Parkland, Florida

The teenager accused of using an AR-15 rifle to kill 17 people at a Florida high school is said to have confessed to police that he was the one who carried out the shooting and carried extra ammunition in his backpack, according to a sheriff's department arrest report.

Nikolas Cruz told investigators that he shot students in the hallways and on the grounds of Marjory Stoneman Douglas High School in Parkland, north of Miami, the report from the Broward County Sheriff's Office said.

The youngest of the victims in one of the deadliest school shootings in US history, was identified as 15-year-old Alyssa Alhadeff. Meanwhile Cruz appeared in court charged with 17 counts of premeditated murder. More than a dozen other people were injured in the shooting. The judge ordered Cruz - who has not yet entered a plea - to be held without bail.

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Police also laid out what they believe to be the timeline for the shooting, which is said to have started when the suspect was dropped off at the school at 2.19 pm local time [7.19pm GMT] by an Uber taxi. Sheriff Scott Israel said at a news conference that the suspect entered the east stairwell and pulled the AR-15 rifle out of a case, readying it and then beginning to shoot into classrooms. The suspect is then said to have shot into classrooms on multiple floors.

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

The suspect is then said to have dropped the rifle, a vest and his backpack before running back down the stairs. Police believe he discarded those items to join others who were fleeing and escape the grounds. Cruz was arrested about an hour later, having visited at least one fast food restaurant in the meantime.

In a televised address to the nation – his fourth following a mass shooting – President Donald Trump urged Americans to “respond to hate with love”.

“Later this month, I will be meeting with the nation’s governors and attorney generals, where making our schools and our children safer will be our top priority,” he said. “We must also work together to create a culture in our country that embraces the dignity of life, that creates deep and meaningful human connections and that turns classmates and colleagues into friends and neighbours.”

In his remarks to the nation, Mr Trump avoided the issue of gun control, which was the subject of a lot of talk from those in Congress throughout the day, but did say he planned to travel to Florida to meet with victims’ families.