US Attorney General Jeff Sessions has defended the Trump administration’s immigration policies while hundreds of protesters rallied outside a conference in Nevada.

Mr Sessions called on Congress to act over the issue and asserted that many children were brought to the border by violent gang members.

Speaking at a school-safety conference in Reno, Mr 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.

He continued: “Get this. More than 80% of the children crossing our borders are coming by themselves, without parents or guardians, often sent with a paid smuggler. We can only guess how many never make it to our border during that dangerous journey.”

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”.

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

Just outside the hotel-casino where he 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 road 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.

Meanwhile, US defence 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.

Defence Secretary Jim Mattis had said on Sunday that two bases had been selected but he would not identify them. Under the arrangement, the Defence 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 its “zero-tolerance” immigration policy until June 9, officials have said.