Dozens of Venezuelan migrants sent by the Trump administration to the U.S. military base in Guantánamo Bay, Cuba, are being guarded by troops rather than civilian immigration officers, according to people familiar with the operation.

While the Trump administration has portrayed the detainees as legally in the custody of Immigration and Customs Enforcement, military guards and medics are doing the work, the people said.

The Trump administration has not released the migrants’ names, although at least two have been identified by their relatives through pictures released of the first flight.

By not disclosing the migrants’ identities, the government has prevented their relatives from learning where they are being held and complicated lawyers’ efforts to challenge their detention.

Spokespeople for the Homeland Security and Defense Departments have been unwilling or unable to answer detailed questions about what is happening to the migrants at the base.

But The New York Times has obtained the names of 53 men who are being held in Camp 6, a prison building where until recently the military held Al Qaeda suspects. The Times has published the list.