A South Texas school district is warning parents that U.S. Border Patrol agents may be checking the immigration status of students as they participate in extracurricular activities. On Wednesday, the Alice Independent School District sent out a letter alerting parents that agents may be boarding school buses to question students about their citizenship status.

Mexican troops arrived in Ciudad Juárez and Tijuana this week and will soon patrol 18 cities near the Mexico-U.S. border.

The Mexican troops will be posted to hot spots along the border with high rates of illegal migration and drug and weapons trafficking.

As soon as the sun glints over miles of border fence dividing the United States and Mexico, the engines of cargo trucks packed with auto and computer parts roar to life along border bridges and bleary-eyed workers file into factories to assemble a multitude of products geared toward the U.