In April, a 54-year-old immigrant from Mexico died after several feverish days in a solitary cell. In May, a 21-year-old man from India hanged himself in an Arizona jail. On June 1, a 25-year-old asylum seeker named Johana Medina Leon died in a Texas hospital after nearly six weeks in the custody of U.S. Immigration and Customs Enforcement.

The deaths of three ICE detainees since April, along with the release of several internal and watchdog reports documenting dismal conditions at ICE detention centers, have prompted an outcry from advocates who say the Trump administration is pushing growing numbers of immigrants into a detention system ill-equipped to care for them.

"What we're seeing is a reckless and unprecedented expansion of a system that is punitive, harmful and costly," said Katharina Obser, senior policy adviser at the Women's Refugee Commission, an advocacy group. "The U.S. government is not even doing the bare minimum to ensure [immigrants] are getting the medical care and the mental health care they need."

Twenty-four immigrants have died in ICE custody during the Trump administration, according to an NBC News analysis of federal data. At least four others, including Medina Leon, died shortly after being released from ICE custody. The number of in-custody deaths remains below the peak of 32 deaths in 2004, the first full calendar year records were kept.

The tally does not include migrants, including five children, who have died in the custody of other federal agencies.

The recent spate of deaths comes as the number of immigrants in federal custody hits a record high. As of early June, ICE was detaining more than 52,500 immigrants a day in a sprawling network of more than 200 detention centers across the country — up from about 34,000 under the Obama administration.

Roxana Hernandez, right, a transgender woman who was part of the caravan of Central American migrants, died in ICE custody at a hospital in Albuquerque, New Mexico, on May 25, 2018. Annie Rose Ramos

Deaths in ICE custody remain "exceedingly rare," an ICE spokesperson told NBC News in a statement. The agency said it spends more than $269 million to provide "comprehensive medical care" to each of the 300,000 to 500,000 individuals who enter its custody each year and reviews the circumstances of all deaths that occur in ICE custody.

ICE "takes very seriously the health, safety and welfare of those in our care, including those who come into ICE custody with prior medical conditions or who have never before received appropriate medical care," said ICE spokesperson Danielle Bennett in a statement. "Any death that happens in ICE custody is a cause for concern."

Immigrants held by ICE are civil detainees, not criminal, and their detention is not intended to be punitive. The Department of Homeland Security's inspector general reiterated that fact in a report released this week that found "egregious violations" at two detention centers it inspected, including nooses in detainee cells, inadequate medical care, rotten food and other conditions that endangered detainee health.

Employees of both DHS and ICE have raised concerns about lapses in medical oversight and neglect that put immigrants at risk of harm or death, according to interviews and internal documents.

Last month, an NBC News investigation found that under both the Obama and Trump administrations ICE has routinely placed immigrant detainees suffering from mental illness or medical issues in solitary confinement. Ellen Gallagher, a DHS policy adviser who was not speaking for the agency, described it as the "widespread abuse of human beings."

In December, an ICE supervisor warned that the ICE Health Service Corps, the agency's own medical service provider, was "severely dysfunctional" and that "preventable harm and death to detainees has occurred," according to an internal memo sent to the now-Director of ICE, Matthew Albence, and obtained by The Young Turks.

The supervisor found staff ignored repeated warnings about a schizophrenic man who later committed suicide in solitary confinement, and that detainees with substance abuse disorders were improperly detoxed.

"IHSC leadership is not focused on preventing horrible recurrences," the supervisor wrote.

An ICE spokesperson did not respond to questions about the memo.

Withdrawal may have contributed to the deaths of at least two detainees since 2017, according to an NBC News review of ICE documents.

One was Kamyar Samimi. Born in Iran, he had lived in the United States since 1976. In November 2017, ICE agents arrested the 64-year-old outside his suburban Denver home due to a low-level cocaine conviction from 2004, which stripped him of his green card.

Samimi was taken to Colorado's Aurora Contract Detention Facility, where the sole physician prescribed medications for withdrawal from methadone, a drug generally used to treat opiate addiction, which Samimi had taken daily for decades.

Samimi was given less than half of the doses of medications prescribed, according to a Detainee Death Review, first obtained by Rocky Mountain PBS. Failure to properly document and administer medication was among 12 different ICE detention standards investigators found the facility "did not fully comply with," investigators found.

ICE investigators have raised concerns about medical care at Aurora before. An investigation several years earlier had found a detainee "did not have access to appropriate medical care" after staff failed to immediately call 911 during his heart attack. Last year, advocates filed a complaint with the Department of Homeland Security, requesting an investigation into what they called "inadequate medical and mental health care" that threatens the "health and well being of its detainees" at the facility.

After Samimi's death, a review by ICE's Office of Professional Responsibility found Aurora's nursing staff was not trained in opioid withdrawal and the facility was short staffed. When Samimi's condition became life-threatening, staff didn't seek emergency care — another deficiency, according to the report.

As Samimi grew worse, he began collapsing, vomiting and screaming out for help. Nurses told officers that they believed Samimi was faking his symptoms. Early one morning, after a severe nosebleed, Samimi asked for ice water. A nurse told him "he could drink water [from the sink] like everyone else." The majority of nursing staff told investigators they "did not see an urgent need" to notify the doctor of his deteriorating health.

Nursing staff told investigators that they were often unable to reach the facility's sole physician, despite ICE policy requiring an on-call physician to be available 24 hours a day. One nurse said the doctor did not have a voicemail set up on his cell phone, and that he returned missed calls "only 50 percent of the time."

The physician never physically examined Samimi. According to his interview with investigators, he only looked at Samimi through a cell door. The doctor said "he believed the detainee engaged in 'behavior to get what he wanted,'" according to the report, and that Samimi's fainting spells were "not legitimate."

Security officers at the facility, however, became increasingly concerned about Samimi's condition. One told investigators he felt that Samimi was "suffering." Several said that they "did not share the opinion voiced to them by nurses that Samimi was faking his symptoms."

A lieutenant told investigators that medical staff often ignored detainee's requests for care. "He shared that he gets a call from an officer almost every night stating a detainee needs to be seen but medical will not come to the unit," the report states.

Samimi died on Dec. 2, 2017, about two weeks after arriving at Aurora. While his cause of death was undetermined, an autopsy found he had suffered from emphysema, gastrointestinal bleeding and that "methadone withdrawal cannot be ruled out as the cause of death."

Days after he died, the facility conducted its own review and found "both medical and security staff acted properly and in accordance with policy and procedures."

"This man should not have died, plain and simple," said Arash Jahanian, an attorney with the Colorado American Civil Liberties Union, which has sued for records regarding Samimi's death. "ICE's own review says there were some serious violations of their own standards for medical care and protocol for how they take care of detainees, and what we would consider basic human decency."

Aurora recently expanded to hold more than 1,500 immigrants for ICE. Problems there persist, said Obser of the Women's Refugee Commission, who visited the facility this April. Obser said detainees interviewed said that medical staff were "unresponsive to requests for medical care."

A spokesperson from GEO Group, the private contractor that operates the Aurora facility, declined to answer questions about Samimi's case. But the spokesperson said that the company has taken measures to correct facility-wide issues identified in a recently-released inspector general report, which included charges of delays in medical care.

"We take seriously any shortcomings in our delivery of consistent, high-quality care, taking immediate action as needed," the spokesperson said.

Neglect in detention isn't limited to one facility, or a single company, said Maureen Belluscio, a senior staff attorney with New York Lawyers for the Public Interest, which recently filed a wrongful death lawsuit against a New Jersey jail and private healthcare provider on behalf of the family of a detainee who died in 2017.

Carlos Bonilla, a father of four, told the medical staff about his liver cirrhosis when he arrived at the Hudson County Correctional Center in April 2017, according to the complaint filed in late May. The local jail, which has for years contracted with ICE to house detainees, has been the subject of several exposes about its medical care.

He had a cough, stomach pain, rash, fever, dizziness, and nose bleeds, according to the complaint, all symptoms of complications from cirrhosis. Bonilla repeatedly "pleaded for medical care," Belluscio said. "Each was an opportunity for someone to do something, but they didn't, and it killed him."

On June 8, 2017, Bonilla was supposed to have a hearing to determine whether he would be released on bond. Instead, he was rushed to the emergency room, where he died two days later of "internal bleeding and hemorrhagic shock."

A spokesman for the Hudson County Correctional Center declined to comment due to ongoing litigation.

NBC News filed a public records request nearly a year ago for the internal death reviews in nearly a dozen cases, including Bonilla's. ICE has yet to release the reports, which are public record.

Those records, along with autopsies, shed light on what can occur in the often opaque detention system, as the three recent deaths show.

When 54-year-old Abel Reyes-Clemente died in a cell in Arizona in early April, an ICE press release pointed to complications from the flu. But the Pinal County Medical Examiner found he died from complications from cirrhosis, diabetes and heart disease, also noting he had tested positive for bacterial pneumonia.

When Simratpal Singh, 21, died a month later, ICE stated in a press release that he was found unresponsive in his cell. The medical examiner in Maricopa County, Arizona, found he died by hanging.

NEW: The El Paso County Medical Examiner is not doing an autopsy on Johana Medina Leon, 25, the Salvadoran trans woman who fell ill in @ICEgov custody and then died in an El Paso hospital. The reason: she was not in custody at the time of her death. 1/ — Bob Moore (@BobMooreNews) June 5, 2019

The cause of death for Medina Leon, the asylum seeker who died on June 1, remains unclear.

Like Roxana Hernandez, a transgender woman who died in ICE custody last summer, Medina Leon was diagnosed with HIV while she was detained.

Medina Leon, known to her friends as "Joa," became ill while detained at the Otero County Processing Center, a private detention center in New Mexico where the ACLU and the Santa Fe Dreamer Project recently alleged poor treatment of, and "unconscionable conditions," for LGBTQ immigrants.

ICE sent Medina Leon to the hospital. The same day she went to the hospital, ICE paroled her, meaning released her from custody. As a result, the agency is not required to issue a press release about her death, nor conduct a death review. The El Paso Medical Examiner told NBC News that it will not conduct an autopsy, which is required for all in-custody deaths.