MEXICO CITY (AP) — Many of the passengers on a bus that tumbled down a steep hillside in western Mexico, killing 18 and injuring nearly two dozen, were migrants headed for Tijuana at the U.S.-Mexico border, Mexican authorities said.

The Nayarit state prosecutor’s office said it had not yet identified the dead from Thursday’s accident, but said they included 10 men, five women and three minors. Mexico’s National Immigration Institute said a Mauritanian citizen was among the deceased.

The prosecutor’s office did identify the 23 injured who were hospitalized. The National Immigration Institute said that among them were two Mauritanian and two Indian citizens. There was also a citizen from the Dominican Republic.

So-called extracontinental migrants have become increasingly common in recent years as they transit Mexico along with traditional migrants from Latin America. They generally fly to a country in Latin America that does not require a visa and then move north toward the U.S. border.

Around 3 a.m. Thursday the bus left the highway near the Nayarit state capital Tepic and tumbled about 40 meters down a steep hillside, according to the state prosecutor’s office. The bus driver has been detained and the preliminary investigation suggests the bus was driving too fast for the curvy road.