Washington: Twenty-one students and an adult were injured when a teenager, armed with knives, attacked students and staff at a high school in the US state of Pennsylvania on Wednesday, officials said.

Cars sit in the parking lot at the scene of a mass stabbing at Franklin Regional Senior High School April 9, 2014 in Murrysville, Pennsylvania. Pic: AFP
Cars sit in the parking lot at the scene of a mass stabbing at Franklin Regional Senior High School April 9, 2014 in Murrysville, Pennsylvania. Pic: AFP