Thousands more migrants are heading toward the U.S.-Mexican border, hoping to gain permanent residency here even as the Trump administration tightens rules on detention and obtaining political asylum.

Some 2,000 migrants arrived in Mexico this week, forcing officials of Chiapas state to declare an emergency. 5,000 more migrants had set out toward the U.S. on Monday, according to the Mexico News Daily.

Meanwhile, "Pueblos Sin Frontreras," a group often cited as being behind the caravans since last year, denied on its Facebook page in a post on Tuesday that it is organizing the large groups and leading them on the long journey to the U.S. border from Honduras, El Salvador and Guatemala.

“Nonetheless, as defenders of human rights of the migrants," the group wrote, "we are in solidarity with the families, children, men and women that see as their only option to flee their communities and migrate.”

Pueblos Sin Frontreras assailed Mexican authorities for what the group says is their failure to honor previous promises to treat the migrants humanely by giving them visitor visas on humanitarian grounds, and are instead adopting a hard line to keep them from getting close to the United States.

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“Mexico is acquiescing to the U.S. and handling this in a law enforcement, rather than humanitarian, manner,” the group said.

Calls to Pueblos Sin Frontreras seeking comment were not returned.

Tensions have flared between the migrants and authorities in countries they pass through, including Mexico.

Central American migrants, part of a caravan hoping to reach the U.S. border, walk on the shoulder of a road in Frontera Hidalgo, Mexico on Friday.The group pushed past police guarding the bridge and joined a larger group of about 2,000 migrants who are walking toward Tapachula, the latest caravan to enter Mexico. (AP)

This week, they tried to push past police, who urged them to stay in makeshift shelters. Officials also told people to stay indoors, warning the migrants were a threat to safety. The town’s cold reception contrasts with the warm welcome it gave to caravans just last year.

More than 7,000 migrants are in Chiapas, according to Mexico News Daily, waiting to receive documents that would allow them to work and live there while they try to apply for asylum in the United States.

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President Donald Trump has called the large numbers of migrants approaching the border an emergency, and has pushed the construction of a wall. U.S. Attorney General William Barr decided Tuesday that asylum seekers who clear a “credible fear” interview and are facing removal don’t have the right to be released on bond by an immigration court judge while their cases are pending. The attorney general has the authority to overturn prior rulings made by immigration courts, which fall under the Justice Department.

Trump also warned Mexico to step up efforts to deal with the groups of migrants trying to get to the U.S., or risk U.S. tariffs on auto imports.

The Associated Press contributed to this report.