Mexico detained more than 650 undocumented migrants, more than half of them children, traveling in refrigerated truck containers towards the border with the United States, authorities said Friday. The military and National Guard on Thursday night “detected three tractor trailers with six long refrigerated containers transporting 652 migrants, of which 355 are minors,” the government of northeastern Tamaulipas state said. Most of the migrants were from Guatemala, and nearly 200 minors were traveling unaccompanied, it said in a statement. Four people transporting the migrants were arrested, it said. The convoy was stopped at a military checkpoint in Hidalgo, Tamaulipas. “Initial information indicates that the migrants came from the city of Puebla (in central Mexico), bound for Monterrey, Nuevo Leon,” in the country’s northeast, the statement said. The announcement came as a top-level delegation from the United States, including Secretary of State Antony Blinken, visited Mexico for talks. Tens of thousands of US-bound migrants from Haiti and Central America have arrived in Mexico in recent months, posing a major challenge to both countries.