At least nine infants under the age of one are being held in a Texas immigrant detention facility, according to a complaint filed on Thursday with the US Department of Homeland Security that warned of an “alarming increase” in how many infants are detained.

Immigrant rights groups have urged the DHS to immediately release the infants and their mothers, who said their children were sick, had lost weight and were crying more than usual.

One of the infants turned six months old in DHS custody at the South Texas Family Residential center in Dilley, where the infants and their families are receiving legal support from the Dilley Pro Bono Project.

The group’s advocacy coordinator, Katy Murdza, said they started noticing infants under the age of one were being held last week. “We’ve almost never seen this before,” Murdza told the Guardian.

It is unusual for US Immigration and Customs Enforcement (Ice), the DHS agency that oversees immigration detention, to detain infants.

Murdza said last year there was an incident where five infants were detained. In the past two weeks, 11 infants were in detention at one time, though two of the children have since been released.

“Most of these babies have been sick and not getting better,” Murdza said. “A lot of moms are saying that they are crying much more than they normally do. They are crying all night and keeping people up in shared dorm rooms. There are a lot of kids who are really congested, sometimes having trouble breathing, coughing a lot.”

Murdza said the mothers, who are Honduran, said they do not always get bottled water with baby formula and they are concerned the detention center’s tap water is not clean enough. The mothers also complained that there have been sudden changes in the formula they are given – even though doctors advise formula to be changed gradually because of infants’ sensitive digestive systems.

At least one of the infants has been detained for more than 20 days, according to the complaint. Under the Flores agreement, it is illegal to hold a child in immigration detention for more than 20 days, though the Trump administration has attempted to modify that rule.

The American Immigration Lawyers Association, American Immigration Council and Catholic Legal Immigration Network, filed the complaint and are partners with the Dilley Pro Bono Project.

In the complaint, the coalition said it had “grave concerns” about the medical care available at the facility for this vulnerable population, in part because of previously documented delays in detainees receiving medical attention and a lack of appropriate follow-up treatment.

Ice said in a statement that the agency provides “comprehensive medical care” to all detained individuals, including registered nurses, licensed mental health providers, a physician and dental care. It said: “Ice is committed to ensuring the welfare of all those in the agency’s custody, including providing access to necessary and appropriate medical care.”

The complaint included a statement from the advocacy group Physicians for Human Rights (PHR) condemning the detention of children in detention centers.

It read: “PHR is alarmed about the inherent health risks for infants in detention, as infants have specific health needs which detention centers are ill-equipped to meet.”

In addition to requesting immediate release of the infants, advocates urged DHS to review any documents showing medical problems the infants have experienced in detention, the medical services that are available and its decisions to detain these infants.