RENO, Nevada (AP) — While hundreds of protesters rallied outside, Attorney General Jeff Sessions defended the Trump administration’s immigration policies Monday, calling on Congress to act and asserting that many children were brought to the border by violent gang members.

Speaking at a school-safety conference in Nevada, Sessions said the crisis at the border is a “difficult and frustrating situation” that requires Congress to act.

“Children have indeed borne much of the burden of our broken immigration system,” he told the National Association of School Resource Officers in Reno.

Sessions said more than 80 percent of children crossing the borders arrive alone, without parents or guardians, and are “often sent with a paid smuggler. We can only guess how many never make it to our border during that dangerous journey.”

He claimed the MS-13 gang “is recruiting children who were sent here as unaccompanied minors, and some are brought to help replenish the gang. And they are terrorizing immigrant schools and communities from Los Angeles to Louisville to Long Island to Boston. They are able to do so because we do not have a secure southwest border.”

The compassionate thing to do, he said, is to protect children from violence and drugs, put criminals in jail and secure borders. He called the alternative, having open borders, “both radical and dangerous.”

He said five children had been found at the border carrying a combined 35 pounds of fentanyl, the powerful synthetic opioid drug blamed for an epidemic of overdose deaths nationwide.

Drug cartels, Sessions said, “take advantage of our generosity and … use children to smuggle their drugs into our country as well.”

Elsewhere, the head of Customs and Border Protection said he had temporarily stopped referring for criminal prosecution adults who cross the border illegally with children.

Commissioner Kevin McAleenan told reporters Monday in Texas that he suspended the referrals within hours of Trump’s executive order last week that stopped the practice of separating families.

He said the “zero tolerance” policy remains in effect, but cases cannot be prosecuted because parents cannot be separated from their children. He said he is working to develop a plan to resume prosecutions.

Just outside the hotel-casino where Sessions spoke, more than 200 protesters opposed to the administration’s immigration policies blocked a busy road. The coalition of civil rights, religious and union activists carried signs and drums and were joined by a mariachi band. Some sat in a busy roadway for while police diverted traffic around them.

The protesters chanted, “Jeff Sessions, you can’t hide. Reno sees your ugly side!” Several carried signs that read “Children are not political” and “Impeach the mad king.”

At least a half-dozen people wearing red arm bands said they intended to get arrested.

The Rev. Karen Foster of the Unitarian Universalist Fellowship said American children are taught to pledge allegiance to the flag “with liberty and justice for all.” She said “there is no justice for thousands of children locked in cages” at the border.

No arrests were immediately reported.

Nearly two dozen Nevada groups tried unsuccessfully last week to persuade the national school law enforcement group hosting the conference to withdraw its invitation to Sessions.

Meanwhile, U.S. defense officials said the administration had chosen two military bases in Texas to house detained migrants. The officials identified the bases as Fort Bliss and Goodfellow Air Force Base. They spoke on condition of anonymity because they were not authorized to speak on the record about a pending announcement.

Defense Secretary Jim Mattis had said on Sunday that two bases had been selected but he would not identify them. Under the arrangement, the Defense Department would provide the land but the operations would be run by other agencies.

As many as 2,300 children were separated from their migrant parents from the time the administration adopted the zero-tolerance policy until June 9, officials have said.

In far West Texas, a temporary tent shelter for immigrant children was close to its 360-person capacity. Reporters were allowed Monday to briefly visit the shelter at the Tornillo border crossing, where more than 320 children ages 13 to 17 are being held.

About half were from Guatemala, and 23 of the children had been separated from adults who accompanied them across the border.

The facility has a current capacity of 360. The tents are air conditioned, and a facility administrator told reporters that the main complaint he hears from children on site is that the tents get too cold sometimes.

Reporters were not allowed to enter any tents holding children. Two girls who stopped briefly in front of reporters said that they were doing well.

The exact process to reunite families has been unclear because migrants are first stopped by Customs and Border Protection. Then children are transferred to the custody of the Department of Health and Human Services, while adults are detained through Immigration and Customs Enforcement, which is under the Department of Homeland Security. Children have been sent to far-flung shelters around the country, raising alarm that parents might never know where their children can be found.

The administration’s policy of criminally prosecuting anyone caught illegally crossing the border remains in effect, officials have said, despite confusion on the ground on how to carry out Trump’s order.

Justice Department officials asked a federal judge to amend a class-action settlement that governs how children are treated in immigration custody. Right now, children can only be detained with their families for 20 days. Trump officials are seeking to detain them together indefinitely as their cases progress. Advocates say family detention does not solve the problem.