NATCHEZ, Miss. — The number of migrants detained by Immigration and Customs Enforcement in the Deep South has quadrupled in the past year, alarming immigration advocates and attorneys who are struggling to keep up.

According to previously unreported ICE data the agency shared with NBC News, the number of detainees in facilities contracted by Immigration and Customs Enforcement in Louisiana and Mississippi surged from just over 2,000 at the end of 2017 to more than 8,000 as of July. That’s nearly four times as many as were detained in the two states in November 2017, the numbers show. Louisiana, with a population of more than 6,500, now has the largest population of ICE detainees of any single state apart from Texas.

Immigration attorneys on the ground say they’re worried about the speed of that expansion, referring to many of the sites as “black holes,” locations brought online for ICE detainees so recently that lawyers say they’ve lost track of their clients for days at a time.

Louisiana and Mississippi are part of a region known as an AOR, or area of responsibility, that falls under the New Orleans Field Office. That area, which also includes Alabama, Arkansas and Tennessee, is now the second-largest sector in the country, according to additional data compiled by ICE and obtained by NBC News.

“It seems like every week we hear of a new detention center which is either being opened or repurposed,” Southern Poverty Law Center immigration attorney Emily Trostle said. When people are moved from one detention center to another, "they oftentimes don't show up in the ICE detainee locator tool online," she said, "so we've experienced many moments of panic where we learn that our clients are being moved. We don't know where or why.”

Trostle is one of just eight attorneys in Louisiana able to represent adult detainees for free in immigration court, according to the Executive Office of Immigration Review’s list of pro bono legal service providers.

She regularly drives nearly two hours from the SPLC office in Alexandria to visit clients in remote, rural areas like the Adams County Correctional Center, just over the state line in Natchez. Out of the 13 facilities now contracted with ICE in the two states, eight came online just this year.

“A client will be moved and it's a panic — we don't know where they're going. And then the deportation officer tells us, ‘Oh, they're being moved to, you know, X, Y, and Z,’ that we didn't even know was being used for ICE detention previously,” Trostle said.

ICE defended the expansion as a response to a surge in border arrivals that began late last year.

"ICE began using new facilities in Louisiana and Mississippi this year to house the increased number of persons encountered at the southern border who are awaiting adjudication of their cases before the federal immigration courts," the agency said in a statement to NBC News.

They added: “Any claim that ICE denies individuals access to legal counsel is false.”

Detained for months at a time

The growing number of ICE detainees here has also come alongside another change.

According to Department of Homeland Security data, the rate of detainees granted parole in the New Orleans AOR has decreased from 75.5 percent in 2016 to just 1.5 percent in 2018, making it the lowest parole rate of any AOR in the country.

In May, the Southern Poverty Law Center sued Department of Homeland Security and ICE officials over the parole rate, accusing the agency of violating its own protocols, which they argue requires the agency to release people who are not a flight risk or a danger to their community.

The lawsuit names a dozen plaintiffs now detained in Louisiana and Alabama, many of whom have been inside for months, some as long as a year.

For family members like Katis, who asked that only her first name be used to protect her brother’s identity, those numbers are personal.

Her brother has been detained in ICE custody for 10 months, and is now in the Adams County Correctional Facility, one of the eight facilities that came under ICE contract this year.

“When they get there it’s like arriving to a cemetery. You don’t have an exit. There’s no answer,” she told NBC News correspondent Morgan Radford in Spanish at her home in Roanoke, Virginia.

In a sworn declaration submitted as part of the law center's lawsuit, her brother says he lived and worked in Cuba as a doctor until 2018, when he fled the country out of fear of violence and political persecution.

“I was forced to flee Cuba after Cuban state officials detained and brutally beat me on multiple occasions because I refused to comply with the Cuban government’s unethical orders,” he said in the declaration, which he dictated in Spanish for translation.

He presented himself at the Laredo, Texas, port of entry and asked for asylum. From there he was transferred to facilities in Texas and Louisiana before winding up at the Adams County Correctional Center.

He was denied asylum in May, then applied for parole, citing his sister’s status as a citizen and his profession as a doctor as proof that he wasn’t a flight risk or a danger. ICE denied that request, which means he will remain in ICE custody for the duration of his appeals.

“We came looking for liberty because it’s supposed to be the country of liberty,” Katis said. “They haven’t even gotten freedom.”

“Es peor,” she added, which means, “It's worse.”