TAPACHULA, Mexico —Thousands of migrants traveling in a caravan toward the U.S. border decided to continue on foot across the isthmus of Mexico Thursday toward Veracruz after an arrangement to travel by bus directly to Mexico City fell through, coordinators announced late Wednesday.

The coordinators blamed the Mexican federal government with blocking a plan to have buses transport migrants to the capital, forcing the caravan to take a well-traveled route through Veracruz that will expose migrants to violent attacks by criminal organizations.

Veracruz is notorious for violent criminal smuggling organizations that seek to extort migrants or sell them to drug-trafficking organizations that seek to enlist or force them to work in the drug trade.

“Today there was the possibility to have 70 buses from various sources of support that under pressure of the Mexican government withdrew their support, leaving the exodus no choice but to continue on foot towards Veracruz, a state of high risk of violence at the hands of criminal organizations,” coordinators said in a written statement.

The migrants rejected taking an alternate route toward Mexico City, through the state Oaxaca, because it would have taken them along curvy mountainous roads through small towns without infrastructure to accommodate such a large group. The caravan, which began its journey Oct. 12 in Honduras, includes many women and children.

Many migrants have become sick along the journey, coordinators noted in their statement.

“Any aggression towards the exodus (of migrants) and those accompany them will be the complete responsibility of the federal government,” the statement said.

In Washington on Thursday, President Donald Trump said he would unveil a plan to limit claims of asylum in the United States, saying there was “rampant abuse” of the system. But he offered no details on the proposal, which was part of a series of immigration announcements he has rolled out in the run-up to next Tuesday’s midterm elections.

Trump said people were taking advantage of the asylum process by making false claims of persecution in order to enter the country. He said many end up staying in the country and fail to show up for court proceedings to determine the validity of their asylum claims.

“My administration is finalizing a plan to end the rampant abuse of our asylum system,” he told reporters at the White House.

President Donald Trump has turned the migrant caravan into a campaign issue for next Tuesday’s midterm elections, and has promised to stop it from entering the U.S.

Members of the binational group Pueblo Sin Fronteras has been coordinating the exodus since it broke through gates in an international bridge and entered Mexico from Guatemala nearly two weeks ago.

The majority of migrants traveling in the caravan are from Honduras, where it formed and exploded in size.

Honduras has a high poverty rate and one of the highest homicide rates in the world Migrants say they are fleeing violent gangs, government corruption, extortion and a lack of jobs.

Migrants with respiratory infections and other illnesses have lined up for assistance from Red Cross workers and other organizations that have been following the migrants from town to town providing medical assistance.

The migrants planned to begin walking toward Matías Romero through the isthmus of Mexico, the narrowest part of the country, after spending a day resting in Juchitán de Zaragoza, a small city in the southern part of Oaxaca near the Pacific Ocean.

On Wednesday, migrants could be seen lining roads and walking through the streets of the city’s crowded center begging for money to buy food, drinks and other necessities.

A second large exodus of Central American migrants forcibly reached Huixtla Thursday about 200 miles south of the main caravan after forcing past Mexican marines and federal police into Mexico on Sunday.

The caravan is more than 1,000 miles from the nearest point on the U.S. border, a distance that could take more than a month for the migrants to traverse.

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