MILWAUKEE (REUTERS) - Staff will return to work on Friday (Feb 23) at the Florida school where a gunman shot and killed 17 people in the deadliest shooting ever at a US high school, district officials said, with students expected back next week.

Marjory Stoneman Douglas High School in Parkland near Fort Lauderdale will also hold a voluntary orientation for students and parents on Sunday and hopes to have students resume classes the following Tuesday on a modified schedule, Broward County Public Schools said in a statement.

Nikolas Cruz, 19, a former student accused of the shooting, made an appearance on Monday in Fort Lauderdale court where he faced 17 counts of premeditated murder.

Cruz is accused of returning to the high school from which he had been expelled and opening fire with an AR-15-style rifle last Wednesday.

The incident has galvanised advocates for stricter gun control, including many survivors of the rampage.

Students, teachers and gun safety advocates plan a visit to the state capital of Tallahassee on Wednesday. They will demand that state lawmakers enact a ban on the sale of assault weapons in Florida.

The suspect, whose mother died in November, was investigated by the authorities after videos surfaced on the social media platform Snapchat, showing him cutting himself, an assessment by the Department of Children and Families said.

In a statement, department secretary Mike Carroll said the records showed Cruz was receiving mental health services before, during and after the assessment. Cruz was living with his mother and attending school when it concluded, he said.

The Federal Bureau of Investigation has acknowledged it failed to act on a tip called in last month, warning that Cruz possessed a gun and the desire to kill.