A caravan made up of about 1,600 migrants from Central America arrived Monday near the border outside of Piedras Negras, Mexico, located across the Rio Grande River from Eagle Pass, Texas.

According to officials, the migrants were detained by the local government in Coahuila state, which arranged for 49 buses from nearby cities Arteaga and Saltillo to safely transport them back into the country's interior.

According to state spokesperson Jose Borrego, the migrants have been kept at an unused factory to block other incoming migrant groups from trying to cross the border. Only those who receive a Mexican humanitarian visitor visa will be allowed to leave the factory premises. 

"We didn’t want to run the risks of them traveling in open trucks," Borrego said.

The Associated Press reported that customs officials on the U.S. side of the border are processing just 12 to 15 visas per day on average and asylum seekers are often turned away.

Reports of the caravan surfaced amid the Department of Defense's announcement to send 250 active-duty troops to Eagle Pass in an effort to aid Mexican authorities and fortify the border. 

The AP noted that the caravan is the first in months to attempt passage through Texas rather than California. 

The detention of the caravan also comes amid President Donald Trump's appeal to Congress to curtail illegal immigration. "Large, organized caravans are on the march to the United States," Trump said in his State of the Union address.

His comments elicited an audible groan from Democrats, as many of the opposing party have accused the president of using migrant caravans as a form of fearmongering

Before the address, Trump tweeted about "tremendous numbers of people" coming up through Mexico "in the hopes of flooding our Southern Border," and made yet another call for his border wall, which the Democrats have flatly blocked at every given opportunity.