The Mexican government has defended its policies, saying that its robust health surveillance system gives it a good idea of how the epidemic is evolving and that health experts are charting the country's fight against the virus.

According to local officials, of the more than 6,150 migrants at the shelter as of Wednesday, 1,068 were children.

Mexico's Interior Ministry said it would immediately deport those who tried to "violently" enter the U.S. from Tijuana.

About 500 Central American migrants headed out of Mexico City on Friday to embark on the longest and most dangerous leg of their journey to the U.S. border, while thousands more were waiting one day more at a massive improvised shelter.

The church has tried to play a mediating role between Ortega's Sandinista government and protesters who have increasingly demanded his ouster amid demonstrations and clashes in which about 450 people — most of them protesters — have been slain.

Nicaragua President Daniel Ortega said he will not move up elections despite street protests that have seen more than 300 deaths in the past three months, but is open to continuing a dialogue mediated by the Roman Catholic Church.

The "Stations of the Cross" caravans began as short Eater-season protests against the kidnappings, extortions, beatings and killings suffered by many Central American migrants as they cross Mexico.

At least 31 priests have been killed in Mexico since 2006.

28 priests have been killed in Mexico since 2006, not counting this week's slayings.

The clashes are the latest flashpoint in an ongoing battle for control of public education in Oaxaca, where the union is resisting government attempts to implement national education reforms passed under President Enrique Pena Nieto.