At least 28 of Marco's fellow immigrant detainees at a privately operated prison in the outskirts of Monroe, Louisiana, have tested positive for coronavirus. The 30-year-old Cuban asylum-seeker believes he could be next, unless he's released.

"There's fear among all of us," Marco told CBS News in Spanish over the phone, referring to other immigrants who are being detained while judges adjudicate their asylum cases. "We are not criminals. We're simply scared. We came here because we have a very real fear of returning to our home countries."

Marco, who asked for his name to be changed, is one of more than 5,500 immigrants in U.S. Immigration and Custom Enforcement (ICE) custody who have demonstrated to an asylum officer a credible fear of being persecuted or tortured in their home countries. Under a binding 2009 internal directive, ICE is generally supposed to parole immigrants like Marco who asked for asylum at an official border crossing, passed their credible-fear screenings and do not pose a public safety threat.

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But under President Trump, parole approvals have plummeted, prompting one federal judge to rule last year that ICE officials in the Deep South could not deny parole to asylum-seekers without considering each case individually.

Even as coronavirus cases inside the nation's immigration jails continue to grow, ICE is not planning to proactively free asylum-seekers like Marco or additional groups of immigrants from U.S. custody, according to congressional aides briefed by the agency. Marco has been denied parole three times in the past two months, most recently on Tuesday, according to documents and his attorney, Lorena Pérez McGill.

At least 287 immigrants detained by ICE have tested positive for the coronavirus, according to agency's latest tally, prompting renewed calls from advocates for the government to oversee a large-scale release of people from immigration detention, which is a civil, not criminal, matter. Monday's spike of 96 cases was followed by 33 new confirmed cases of infected detainees on Tuesday and 34 on Wednesday.

As of Tuesday, ICE had conducted 425 coronavirus tests among the tens of thousands of immigrants in its custody, agency officials told CBS News.

Detainees have grown increasingly frustrated in recent weeks. In March and April, there were at least 5 incidents in Texas, Georgia, Arizona and Louisiana in which detention center staff used pepper spray on protesting immigrants, according to ICE officials, who said the "calculated use of force" mitigates risks of injury for both staff and detainees.

In a briefing last Friday, acting ICE Director Matthew Albence repeatedly told lawmakers on the House Committee on Oversight and Reform that a review of potentially vulnerable detainees had ended and there are no plans to expand the categories of immigrants who could be freed beyond older immigrants, pregnant women and those with certain medical conditions. Several Democratic congressional aides who were on the call described Albence's comments to CBS News.

Earlier in the month, ICE announced it would consider releasing detainees who were over the age of 60 or pregnant. The agency later instructed officials to also identify detainees with certain underlying medical conditions, like lung disease and severe asthma, for potential release, according to a directive to detention centers. The agency made nearly 700 releases under these guidelines, according to ICE and congressional officials.

According to Pérez McGill and a Cuban medical certificate, Marco suffers from "bronchial asthma." His wife is also in the U.S., which Pérez McGill said shows he has the community ties required for being paroled.

But in its last parole denial, ICE said Marco could be a flight risk because he has not demonstrated "substantial ties to the community." In a recent email reviewed by CBS News, an ICE official also said the agency is not releasing "cases that have appeals pending" or "detainees for COVID-19 without significant medical documentation." Marco is appealing an asylum denial by an immigration judge, according to Pérez McGill.

ICE's detention population has dropped recently, reaching less 32,000 last week, according to a recent court filing. During the briefing on Friday, Albence said detention space is "under capacity" and that the detainee population had plummeted by 65% since March 20, the staffers on the call said. But Albence said the dramatic drop stems from the fact his agency is receiving fewer migrants from border officials and apprehending fewer immigrants in the interior of the country, the aides added.

Under a temporary public health order that was extended on Monday, border officials have been expelling thousands of unauthorized migrants and asylum-seekers, including unaccompanied children, instead of processing and detaining them under U.S. immigration law. No migrants in Customs and Border Protection custody have tested positive for the coronavirus, a senior agency official told CBS News Wednesday.

ICE has also scaled back its immigration enforcement in the interior of the country in response to the pandemic. Albence said Friday his agents are now focusing on arresting "violent and aggravated felons who pose an immediate public safety risk," congressional aides said.

According to the aides, lawmakers asked Albence if the agency would consider releasing other immigrants, including the thousands of asylum-seekers who have passed their credible fear screenings. Albence made it clear that no further releases were planned and grouped asylum-seekers with immigrants the agency says it is required to detain under law because of criminal convictions, the congressional aides said.

ICE did not respond to multiple requests to provide more details about the agency's current release policy. An ICE spokesperson said one of the agency's main priorities is the well-being of detainees.

"We have been taking important steps to safeguard all detainees, staff and contractors, including: reducing the number of detainees in custody by placing individuals on alternatives to detention programs, suspending social visitation, incorporating social distancing practices with staggered meals and recreation times," the spokesperson said, adding that new detainees are being isolated for 14 days.

On Monday, a federal judge in California ordered ICE to rapidly review the cases of all detainees at increased risk of severe illness or death if they contract the coronavirus and determine whether they should be released. The order expanded the categories of immigrants ICE has already evaluated for release by lowering the age of vulnerable detainees to 55 and defining all the medical conditions that could pose a risk of severe complications.

It's unclear how many immigrants could be released under this order. An ICE spokeswoman said the agency, as matter of policy, does not comment on litigation. "However, lack of comment should not be construed as agreement with or stipulation to any of the allegations," the spokeswoman added.

During last week's briefing, Albence was asked about the relatively low number of tests, according to congressional aides. Albence suggested the agency would be doing more if it had more test kits, the aides said. Advocates have criticized ICE for not testing more detainees, saying the agency would be reporting more positive cases if it was screening more people.

Members of Congress also pressed Albence last week on the number of migrants who have tested positive for coronavirus after being deported by his agency, according to congressional aides. Albence cast doubt on the reports of large numbers of deportees testing positive in Guatemala, the aides added.

At least 51 migrants recently deported by the U.S. to Guatemala have tested positive for coronavirus, according to Guatemalan public health ministry officials. Cases among deportees have also been reported in Mexico and Haiti, the poorest country in the Americas. In response to the large number of infections among deportees, which make up more than 16% of the country's total cases, Guatemala has indefinitely suspended deportation flights last week.

Albence confirmed to members of Congress that his agency is not routinely testing migrants for coronavirus before deporting them, congressional officials said. ICE has said it conducts temperature checks on would-be deportees, not allowing immigrants with a temperature of 99 degrees or higher to board flights and referring them to further medical evaluation, as fever is one of the main symptoms of COVID-19. Before that policy was implemented last week, the temperature threshold was 100.4 degrees. The administration has also tasked a Centers for Disease Control and Prevention team to "review" the tests Guatemalan officials are conducting on deportees.

Last week, ICE stopped detaining immigrants at the deportation staging facility in Alexandria, Louisiana, to "stem potential spread of COVID-19," an agency spokesperson said. At least 14 of the 32 direct ICE detention center employees who have tested positive for coronavirus work at the deportation hub in Alexandria. The agency has not been reporting cases among private contractors, who oversee most detention facilities.

The ICE spokesperson said the agency has been transporting immigrants to the airport in Alexandria and deporting them without holding them at the detention facility there.