MIAMI (AFP) - Nikolas Cruz, the man accused of shooting dead 17 people in a Florida high school, is facing new charges for allegedly tackling and assaulting a jail guard and taking his stun gun, according to an arrest report.

Cruz, 20, has been in custody since shortly after the Feb 14 attack in Parkland, north of Miami, one of the worst school shootings in US history.

He is currently awaiting trial, with prosecutors indicating they will seek the death penalty.

The new charges include assault, battery, and use of a weapon against a law enforcement officer.

The fight broke out on Tuesday evening when an officer identified on the arrest report as Sergeant Beltran asked Cruz to "not drag his sandals around" while walking in the jail's dayroom.

Cruz responded by showing the guard his middle finger, the report said.

As Beltran rose to stand, Cruz rushed towards him and struck him, whereupon a struggle ensued and the guard fell to the ground.

The report cited video footage which showed Cruz using his right fist to strike Beltran several times on the head before pulling the guard's stun gun from its holster.

The weapon "can be seen discharging" as the two men struggled for it, with Beltran eventually regaining control.

Beltran then struck Cruz on the face, causing him to retreat to one of the seats in the dayroom area, at which point he was taken back into custody.

Cruz rose to national infamy following the attack on the Marjory Stoneman Douglas High School.

Footage recovered from his phone showed he had filmed his plans to attack his former school, saying his goal was to kill "at least 20 people."

He also told a detective after his arrest he heard demons ordering him to "buy weapons, kill animals and destroy everything."

Student survivors of the massacre have since become leading advocates for tougher gun control, spearheading marches around the country, but Congress has yet to legislate significant reform.