A formal complaint has been lodged against the Department of Homeland Security with at least 10 migrant mothers accusing the agency of serious neglect and poor treatment of women and children thrown at family detention centres.

Advocacy group Catholic Legal Immigration Network (CLINIC), one of the six organisations that filed the complaint, alleged that the mothers received substandard care while staying at three family detention centres in Texas and Pennsylvania.

CLINIC Executive Director Jeanne Atkinson also claimed that women and children have "inadequate access to and quality of care, a lack of opportunity for informed consent, inadequate oversight and accountability, and questionable medical ethics."

"The overarching issue here is that you have traumatised women and children, and that detention I think is increasing the trauma and the negative physical and mental health effects that come with that, coupled with a health service that is not capable of providing for the needs of these women," Atkinson said, according to Catholic News Agency.

The complaint was filed almost two weeks after a coalition of lawyers providing pro bono services to undocumented immigrants held in two family detention facilities in Texas delivered a scathing letter to immigration officials on July 27.

Lawyers from CLINIC, American Immigration Lawyers Association (AILA), and Refugee and Immigrant Center for Education and Legal Services (RAICES) were addressed to Immigration and Customs Enforcement Director Sarah Saldaña.

They demanded Saldana to "account for the cascade of due process violations at detrimental practices" at the family detention centre in Dilley and the other in Karnes City, Texas.

The advocacy groups' representatives also alleged that agency officials denied undocumented immigrants access to legal counsel, coerced them into wearing ankle monitors, and did not offer clear or adequate information on the terms of their release.

Citing RAICES volunteers who interviewed women released at a bus station in San Antonio, the lawyers also alleged immigrants did not understand the details concerning their release.

They said the illegal immigrants were given instructions to report for an upcoming court hearing to determine whether they are eligible to stay in the United States, and could meet with a lawyer for the time being to prepare their cases.

Gillian Christensen, press secretary of Immigrations and Customs Enforcement (ICE), vowed the agency would review the claims and "respond directly to AILA."

"ICE takes very seriously the health, safety and welfare of those in our care. The agency is committed to ensuring that individuals housed in our family residential centres have care and resources," Christensen said, according to the Los Angeles Times.

"DHS has determined reconsideration is appropriate for custody decisions of arriving families who have established eligibility for asylum or other relief under our laws. Understanding the sensitive and unique nature of housing families, ICE is evaluating cases of residents at the agency's family residential centres," he added added.

The spokesperson also assured that ICE will generally not detain mothers with children if there is no threat to public safety or national security, or if they have received a positive finding for credible or reasonable fear, and if the individual has provided a verifiable residential address.