Updated at 6:10 p.m. with details from police.

Two Richardson High School students were taken into custody after a threat against the school was found scrawled on a bathroom mirror Thursday, officials said.

The students, a 15-year-old sophomore and a 16-year-old freshman, face a charge of making a terroristic threat, Richardson police said.

The message was a threat to shoot up the school at 3 p.m., district spokesman Chris Moore said.

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Richardson was threatened to shoot up the school today around 1 and we are currently in lock down, they aren’t allowing parents to pick there kids there is The PD is everywhere. pic.twitter.com/nRs8LVtlxC — ☆ fridac ☆ (@FridaCardona_) February 22, 2018

The campus was placed on lockdown in response to the threat around 1:30 p.m., Moore said. The district announced the lockdown was over in a tweet at 2:41 p.m.

Richardson police recommended the lockdown as a precautionary measure, principal Chris Choat wrote in a letter on the school's website.

During the lockdown, students were asked to shelter in the classrooms they were in at the time, Moore said. Students in areas like the library or the cafeteria at the time were moved to a secure room, he said.

Parents weren't allowed in the building while it was under lockdown, the district wrote on its Facebook page. Richardson police and district security will continue their presence on campus Thursday and Friday, the district said.

This week, seven students around the Dallas-Fort Worth area have been detained after making threats against their schools or bringing guns to campus. One of those threats, at Arlington High School, referenced the Parkland, Fla., shooting at Marjory Stoneman Douglas High School in which 17 people were killed.

The day after the Parkland shooting, five Dallas-area students were detained for similar threats or for bringing guns to school.