Rabat, Morocco — Four Moroccan truck drivers went missing Saturday as they crossed the restive border area between Burkina Faso and Niger, according to a source from the Moroccan Embassy in Burkina Faso and a Moroccan transport union. Three trucks, one carrying a spare driver, disappeared as they drove without an escort from Dori in Burkina Faso to Tera in Niger, an area known for jihadi threats, the diplomatic source said. Junta-led Burkina Faso and Niger are battling Islamist militant groups linked to al-Qaida and Islamic State, whose insurgencies have destabilized Sahel states in West Africa over the past decade.