Between 250 and 300 migrants marched overnight to a point midway across the Gateway International Bridge between Matamoros, Mexico, and Brownsville, Texas, sitting in the vehicle lanes and blocking traffic in both directions for about 15 hours.

Customs and Border Protection halted traffic across the Gateway bridge and another international crossing nearby about 1:30 a.m., an agency spokesman said, in response to protesters who were not carrying documents for legal entry into the United States.

Traffic resumed before dawn at the second crossing, but the Gateway bridge remained closed in both directions until late afternoon on Thursday, the spokesman said, with all vehicle traffic diverted to other ports of entry.

The episode unfolded amid escalating tension over the Trump administration’s increasingly rigid policies aimed at restricting the entry of migrants into the United States. The Gateway bridge is adjacent to a teeming encampment where about 1,000 migrants, mainly from Central America, have been living in squalid conditions while they await immigration court hearings in the United States.

In recent interviews, families have described children falling ill, families plagued by thugs and a growing sense of despair as U.S. authorities continue to send people back from the border.

“They are absolutely desperate, with no international presence in the camp to organize anything such as food delivery or medical care,” said Jodi Goodwin, an immigration attorney who holds regular workshops to help migrants fill out asylum applications and learn about the legal process.

The migrant protest, which included children, occurred as the Trump administration is moving to contain a record-breaking surge in migrant families, with the biggest numbers crossing into South Texas.

Border authorities took nearly 1 million people into custody in the fiscal year that ended Sept. 30, the highest number since 2007. But the new restrictive measures have brought about a sharp decline, with Customs and Border Protection reporting this week that about 52,000 migrants were taken into custody in September, an 18% decrease from August.

For decades, those who could reasonably argue they were fleeing persecution in their homelands could enter the United States and wait for their hearings in court. Often they stayed with relatives in the interior of the country.

But under a Trump administration program introduced in January, many migrants seeking admission to the United States are now being sent back to Mexico for the duration of their court proceedings. They are allowed to cross the border only for their hearings, often conducted in an expanding network of tent courts.

The migrants’ chances of gaining entry into the United States were further impaired last month when the Supreme Court let stand another new Trump administration policy that requires migrants who traveled through other countries en route to the United States to prove they had been denied asylum along the way before being eligible to apply at the border.

More than 50,000 migrants have been sent back from various southern border entry points, including about 120 a day who are being returned to Matamoros.

Not only has the plaza encampment near the bridge in Matamoros grown more crowded by the day, say volunteers who have worked with the group, but in a town that is notorious for drug and gang violence, some migrants have been victims of kidnapping for extortion and sexual assault.

Thursday’s protest at the bridge was peaceful, witnesses said. By early afternoon about 150 migrants remained, despite reminders by the authorities that the protocols for admission would not be waived. After a visit by immigrant advocates and the mayor of Matamoros, they dispersed in the late afternoon and the lanes reopened to traffic.

The Gateway bridge closure had caused long lines to form at two other international bridges leading into Texas, and border officials said Thursday’s scheduled immigration court hearings in Brownsville were postponed.

Emigdio Manuel García, 89, who owns a restaurant and curios shop in Matamoros about a block from the bridge, expressed exasperation over the disruption caused by the closure. “These people have been here for many months,” he said. “They are now invading the international bridge to protest and they are blocking passage.”

Garcia said the bridge was vital to the economy of both cities. The shutdown, he said, affects “people who are trying to get their kids to school, who are trying to go shopping.”

“Matamoros and Brownsville are one single city, a city joined by a bridge that is now dividing us,” he added.

There have been attempts by migrants to rush two other international bridges in South Texas in recent months. In June and July, authorities at the Hidalgo-Reynosa International Bridge intercepted a handful of migrants trying to run across. Several migrants also attempted to get across the bridge connecting Reynosa, Mexico, and Pharr, Texas.

In November last year, a peaceful march by Central American migrants waiting in Mexico across from California veered out of control as hundreds tried to evade a Mexican police blockade and run toward the border crossing into San Diego.

In response, U.S. authorities shut down the border crossing in both directions and fired tear gas to repel migrants, most of whom had been traveling as part of a large caravan.

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