Pediatricians have released disturbing pictures drawn by migrant children depicting themselves behind bars in detention facilities.

The drawings are by three children, aged 10-11, released last week from Customs and Border Protection custody.

"The fact that the drawings are so realistic and horrific gives us a view into what these children have experienced," Dr Colleen Kraft, former president of the American Academy of Pediatrics, told CNN.

Thousands of children are detained by the US after being separated from their parents or guardians at the US-Mexican border.

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Pediatricians have released disturbing drawings by migrant children depicting themselves behind bars after being taken into detention by US officials.

The pictures were drawn at the Catholic Charities Humanitarian Respite Center in McAllen, Texas, by three unaccompanied children aged 10 to 11, who were released last week from custody by US Customs and Border Protection (CBP).

They were handed by a social worker to news organisations, and depict sad figures held behind bars or fences and watched by guards.

A drawing by migrant children recently released from CBP depicting their time spent in U.S. Customs and Border Protection (CBP) custody. Courtesy American Academy of Pediatrics/Handout via REUTERS

"The fact that the drawings are so realistic and horrific gives us a view into what these children have experienced," Dr Colleen Kraft, former president of the American Academy of Pediatrics, told CNN.

"When a child draws this, it's telling us that child felt like he or she was in jail."

Government figures show that on any one day around 2,000 unaccompanied children are being held in CBP centers.

A drawing by migrant children recently released from CBP depicting their time spent in U.S. Customs and Border Protection (CBP) custody. Courtesy American Academy of Pediatrics/Handout via REUTERS

Under current rules, migrant children are not supposed to be held for more than 72 hours by US officials before being handed over to social workers, but in reality some children are being held in centers for weeks without proper care, food or access to showers.

AAP pediatricians claim they are being denied access to treat children at CBP facilities, and offers to train agents to screen children for illnesses have been refused.

"Children do not belong in Customs and Border Protection facilities, or in any detention facilities," Dr. Sara Goza of the AAP told NBC News Wednesday. "No amount of time spent in these facilities is safe for children."

The CBP spokesperson told CNN in June that under a January directive a credentialed healthcare provider is supposed to assess every child taken into custody.

"We have about 85% coverage now by our current contract, nurses and RNs who are in our intake center, 24 hours a day, seven days a week," the spokesperson said.

The US government in late June said it was rehousing 300 migrant children who had been detained in a remote border patrol station near El Paso, Texas, after attorneys inspecting the facility found older children taking care of infants and toddlers, and children who had not washed in weeks.

100 migrant children were subsequently moved back into the station.

Doctors warned last summer that children being separated from their parents at the border under President Trump's "zero tolerance" migration policy faced long-term health risks, including asthma, obesity, cancer, and mental health issues.

The president ended the child separation policy after a domestic and international outcry, but thousands of unaccompanied children are still being held in CBP facilities after trying to enter the US alone or with relatives other than their parents.