A 42-year-old man being held at the Nassau County Jail as an ICE detainee was found dead in his cell early Thursday morning, according to sources.

Sources tell News 12 the man — who has not yet been publicly identified — was discovered unresponsive and not breathing about 18 hours after arriving at the jail. Early indications suggest he died in his sleep, and sources say he suffered from serious underlying medical issues.

The man was being held under a partnership between Nassau County and U.S. Immigration and Customs Enforcement (ICE), under which the county provides 50 jail cells for immigration detainees and receives federal reimbursement in return.

In a written statement, Nassau County Sheriff Anthony LaRocco said:

“There is an ongoing investigation which will be thorough and transparent to determine the cause of death. Nassau County takes seriously its obligation to treat every prisoner humanely.”

Still, the incident has raised concerns among advocates and local officials, who are demanding answers about the health and safety conditions within the jail — particularly for immigration detainees.

Luis Mendez, of the advocacy group Empowering Young Professionals, questioned the facility’s standards of care:

“What’s going on in the jail? I think that’s the bigger question. Are inmates safe? Are they being provided healthcare properly?”

Serena Martin-Liguori, executive director of New Hour Long Island, called the death "absolutely unacceptable."

“The Nassau sheriff can make a priority to ensure that people, whoever is there, are kept safe," said Martin-Liguori.

Nassau County Legislator Seth Koslow, who is currently running for county executive, has called for a legislative hearing into the incident.

Additionally, the New York State Attorney General’s Office has launched its own investigation.