As the Trump administration continues to defend its new “zero tolerance” policy on immigration, audio has reportedly revealed the cries of immigrant children hours after they are separated from their families at the US border.

“Mami!” one child can be heard crying in the seven-minute audio. “Papá!” another screams.

“Well, we have an orchestra here,” says a man identified as a Border Patrol agent. “What’s missing is a conductor.”

The audio reportedly comes from inside a US Customs and Border Protection detention facility, where migrant children are held as their parents face prosecution for crossing the border illegally.

Under the Trump administration's new zero tolerance policy, all adults caught crossing the border illegally are required to face criminal charges – a process that inevitably separates them from any children they bring with them.

Nearly 2,000 children have been separated from their parents since the zero tolerance policy began in April, according to the Department of Homeland Security (DHS). More than 100 of them were under the age of four.

The new audio captures the reactions of 10 of these children after they were separated from their families, according to ProPublica, which published the recording on Monday.

The children can be heard sobbing and calling out for their parents. One girl, identified as six-year-old Alison Jimena Valenica Madrid, can be heard reciting the number of an aunt in the US and begging detention centre employees to call her.

The aunt later told ProPublica that receiving the anguished call was “the hardest moment in my life”.

“Imagine getting a call from your 6-year-old niece,” said the woman, who is also applying for asylum in the US. “She’s crying and begging me to go get her. She says, ‘I promise I’ll behave, but please get me out of here. I’m all alone.’”

DHS did not respond to The Independent's request for comment.

Undocumented immigration across the US-Mexico border Show all 14 1 /14 Undocumented immigration across the US-Mexico border Undocumented immigration across the US-Mexico border Immigrant children, many of whom are separated form their parents, are housed in Texas' tent city Reuters Undocumented immigration across the US-Mexico border A two-year-old Honduran asylum seeker cries as her mother is searched and detained near the US-Mexico border Getty Undocumented immigration across the US-Mexico border Undocumented migrants ride on the top of a freight train referred to as the beast, or La Bestia Getty Undocumented immigration across the US-Mexico border A cage inside a US Customs and Border Protection detention facility in Texas Reuters Undocumented immigration across the US-Mexico border US Border Patrol Academy All new agents must complete a months-long training course at the New Mexico facility before assuming their posts at Border Patrol stations, mostly along the US-Mexico border Getty Undocumented immigration across the US-Mexico border US-Mexico border fence A group of young men walk along the Mexican side of the US-Mexico border fence in a remote area of the Sonoran Desert Getty Undocumented immigration across the US-Mexico border US-Mexico border fence in the US Man looks through US-Mexico border fence into the US in Tijuana, Mexico Getty Undocumented immigration across the US-Mexico border US-Mexico border fence US Border Patrol agent Sal De Leon stands near a section of the US-Mexico border fence while stopping on patrol on in La Joya, Texas Getty Undocumented immigration across the US-Mexico border US Border Patrol Academy US Border Patrol instructor yells at trainees after their initial arrival to the academy Getty Undocumented immigration across the US-Mexico border Memorial service in Guatemala Families attend a memorial service for two boys who were kidnapped and killed in San Juan Sacatepequez, Guatemala. Crime drives emigration from Guatemala to the United States, as families seek refuge from the danger Getty Undocumented immigration across the US-Mexico border Arrests on the border Undocumented immigrants comfort each other after being caught by Border Patrol agents near the US-Mexico border Getty Undocumented immigration across the US-Mexico border Detention holding facility A boy from Honduras watches a movie at a detention facility run by the US Border Patrol Getty Undocumented immigration across the US-Mexico border Mexican farm workers Mexican migrant workers harvest organic parsley at Grant Family Farms in Wellington, Colorado Getty Undocumented immigration across the US-Mexico border Mexican family in Arizona A Mexican immigrant family sits in the living room of their rented home in Tuscon, Arizona. The family that Arizona's new tough immigrant law had created a climate of fear in the immigrant community. Getty

The UN’s top human rights official has likened the situation at the border to child abuse, and the American Association of Paediatricians has said it could cause “irreparable harm.” Former Republican First Lady Laura Bush decried the practice in an editorial over the weekend, comparing it to the internment of Japanese Americans during WWII.

But Homeland Security Secretary Kirstjen Nielsen continued to defend the zero tolerance policy at a White House press briefing on Monday. She claimed the children in DHS custody were being being “well taken care of” and receiving meals, medical care, and educational services.

The secretary blamed Congress for the family separations, saying the administration was only enforcing existing laws that require children to be released quickly from DHS custody – laws that do not apply to their parents.

"This administration did not create a policy of separating families at the border,” she said. “What has changed is that we no longer exempt entire classes of people who break the law.”

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Congress is currently considering several immigration bills, including a Democrat-sponsored initiative that would prohibit separating families unless agents suspect abuse or child trafficking. A White House-backed bill would end the Diversity Visa Program and reduce the number of family-based immigration visas, while offering a path to citizenship for people brought to the country illegally as minors.

Congress is expected to vote on the measures later this summer. In the meantime, only Mr Trump has the power to unilaterally reverse the zero tolerance policy – an option Press Secretary Sarah Huckabee Sanders said he would not be taking.