TO GO WITH AFP STORY BY CAROLA SOLE Mexican Immigration Service agents detain migrants travelling on a train during an operation to stop illegal Central American migrants in the San Mateo community in Palenque, Chiapas State, Mexico, on June 20, 2015. Hundreds of Central American migrants arrive in Mexico on their way to the United States. AFP PHOTO/ALFREDO ESTRELLA (Photo credit should read ALFREDO ESTRELLA/AFP via Getty Images)
