A caravan of Central American and South American migrants headed to the U.S.-Mexico border has been halted in southern Mexico, held up by sickness and violence.

Between 2,000 and 3,000 migrants departed the Guatemala-Mexico border headed north on foot nearly two weeks ago. The group was walking through the Mexican state of Chiapas on its way to Mexico City, 800 miles away, but was blocked from continuing out of Chiapas by the Mexican military, as well as a mosquito-borne illness that has led to hospitalizations of children in the group, according to the Mexican government’s National Institute of Migration.