Two teenage girls in the US state of Texas have been arrested for plotting a "mass casualty attack" with pipe bombs and guns, police say.
The girls, ages 15 and 16, were planning an attack at Memorial High School in a suburb of Houston, police told KHOU, an affiliate of the BBC's US partner CBS News.
The plot - which was shared on social media - was detailed enough that officials deemed it to be credible, CBS reported.
The Federal Bureau of Investigation (FBI) said its Threat Mitigation Team was involved in the response to help local police arrest the teenagers immediately.
"We are treating this matter with the utmost urgency and commitment, as threats of violence in our schools will not be tolerated," the Montgomery County Sheriff's Office said in a statement.

Two Texas teenage girls arrested for 'mass casualty attack' plot
The high school students were planning an attack with pipe bombs and guns, police say.
