U.S. authorities are transferring into federal prisons about 1,600 Immigration and Customs Enforcement (ICE) detainees, officials told Reuters on Thursday, in the first large-scale use of federal prisons to hold detainees amid a Trump administration crackdown on people entering the country illegally.

An ICE spokeswoman told Reuters five federal prisons will temporarily take in detainees awaiting civil immigration court hearings, including potential asylum seekers, with one prison in Victorville, California, preparing to house 1,000 people.

Officials of a prison employees' union said the influx of ICE detainees, who were arrested at the border or elsewhere in the United States by immigration officials, raises questions about prison staffing and safety.