Several weeks ago DeSaulnier asked California Attorney General Xavier Becerra to look into the ICE detainee claims.

Earlier this month an advocacy group released a letter signed by 27 ICE detainees at the jail, alleging inhumane conditions. That came after supporters of female inmates said they were confined to cells with no toilets, had to wait for jail staff to let them use a shared bathroom at a scheduled time or relieve themselves in plastic bags.

The San Francisco Chronicle reported that after the letter was released, inmates claimed their treatment got worse.

The Contra Costa County Sheriff's Office disputes the ICE detainee claims and on Monday Sheriff David Livingston pushed back even harder, reiterating that the department's own investigation into the allegations is already underway.

"Congressman DeSaulnier toured our facility and was invited to view any area he wished to visit and speak to any detainee he liked," Livingston said in an emailed statement through a spokesman. "He can now publicly call for any additional investigation he wants.

"However, as the political rhetoric from some around this issue continues to boil, we remain undeterred in providing professional and diligent custody services of our county inmates and federal detainees. We are responsible for over 1,600 inmates every day, day-in and day-out, and the allegations of the few ICE female detainees are a fraction of this number."

A Justice Department spokesman declined to comment on DeSaulnier's concerns.

An ICE spokesman has said the jails that hold immigration detainees are subject to rigorous standards and regular inspections.

"I wanted to see for myself," DeSaulnier said.

Livingston took the congressman on a 90-minute tour of the facility, along with two other high-ranking officials with the department. DeSaulnier met afterward with inmate advocacy groups.

"It was a first look," DeSaulnier said. "Just by going through physically one time, you can't tell what might have happened, individually."

"I'm looking forward to getting to the bottom of it," he said. "If something's gone wrong, people will be held accountable."

Read Rep. DeSaulnier's letter to U.S. Attorney General Jeff Sessions below: