Image copyright US Customs and Border Protection Image caption The authorities released this image of illegal migrants inside a large cage - reporters said they saw unaccompanied children in similar conditions

Reporters and Democratic lawmakers have been allowed inside a detention centre that lies at the heart of a growing storm over a new US policy separating migrant children from their parents.

Authorities did not allow photos or videos to be taken inside the centre, but US Customs and Border Protection later released several images. Former First Lady Laura Bush has compared it to the internment camps used for Japanese-Americans during World War Two. A Democratic congressman who visited the site said it was "nothing short of a prison".

The Texas facility is known as Ursula, though immigrants are reportedly calling it La Perrera - dog kennel in Spanish - in reference to the cages used to hold children and adults who have ended up there after crossing the border from Mexico illegally.

"One cage had 20 children inside. Scattered about are bottles of water, bags of chips [crisps] and large foil sheets intended to serve as blankets," the Associated Press reports.

Image copyright US Customs and Border Protection Image caption This image from the US Customs and Border Protection shows the foil blankets given to children

Democratic Senator Jeff Merkley led the team of lawmakers to the site in the town of McAllen on Sunday.

He hit the headlines earlier this month when he was turned away from another facility housing some 1,500 boys in a disused Walmart store.

Speaking to CNN after the visit to Ursula, he said: "In wire-mesh, chain linked cages that are about 30x30 [feet], a lot of young folks put into them.

"I must say though, far fewer than I was here two weeks ago. I was told that buses full (of children) were taken away before I arrived.

"That was one of my concerns, that essentially, when you have to give lengthy notice, you end up a little bit of a show rather than seeing what's really going on in these centres."

Maryland Senator Chris Van Hollen and Vermont Congressman Peter Welch expressed shock and anger over the conditions they saw:

Inside Ursula, more than 1,100 illegal immigrants are waiting to be processed. They have been separated into three wings: unaccompanied children, lone adults and parents with their children. Officials said nearly 200 of those being held there were unaccompanied minors and another 500 were parents with their children.

The Los Angeles Times, which also sent a team there, described the 72,000 sq ft facility as "clean and spare, with bare concrete floors".

A patrol agent currently in charge of the site, John Lopez, told the paper the 42 portable toilets on site are cleaned three times a day. There are three paramedics, two medical members of staff and 310 employees - but no mental health staff, or training, the paper notes. The main lights in the building remain on at all times.

Read more on US migrant family separations:

Nearly 60 miles away, in the town of Brownsville, some 1,500 boys are being housed inside a building that was once a Walmart superstore. The boys, aged 10 to 17, were all caught illegally crossing the border. It is America's largest facility for such minors, and numbers have increased in the past month by several hundred.

Senator Merkley's Facebook Live on 4 June showing security officials denying him entry to that site - known as Casa Padre - led to questions about conditions there. Last week, news organisations were given a tour.

Media playback is unsupported on your device Media caption Zero-tolerance: The US policy dividing families and opinion

No cages were mentioned, but the accommodation was likened to dorm rooms inside a giant warehouse. To accommodate for the growing numbers since the new "zero-tolerance" policy went into force, cots have been added to sleeping areas in the Casa Padre.

The New York Times described it as "clean, massive and brightly lit", with the children given classes six hours each week day and outdoor play time for two hours a day. They have 48 medical staff and three on call doctors on hand.

Long-term trauma?

"Those kids inside who have been separated from their parents are already being traumatised," Senator Merkley warned. "It doesn't matter whether the floor is swept and the bed-sheets tucked in tight."

Officials say they are trying to keep siblings together and not separate children under four or younger from their parents.

But Anne Chandler, who's running a non-profit project for migrant children found on the southern US border, told Texas Monthly she had heard stories of "kids that are very young, that are breastfeeding babies and under three in the shelters, separated from their parents".

The head of the Tahirih Justice Centre in Houston said she had seen cases where parents had not been told ahead of time that their child was being taken away, and instead were told by immigration officers that their child required a bath, only to not be returned.

"I was talking to one mother, and she said, "Don't take my child away," and the child started screaming and vomiting and crying hysterically, and she asked the officers, "Can I at least have five minutes to console her?" They said no," Ms Chandler told the magazine.

Image copyright AFP Image caption Authorities say they do not separate parents with children under five

A rights worker who visited the Ursula facility at the weekend told the Associated Press she had spoken to a 16-year-old girl who was left in charge of an unaccompanied toddler for three days and tasked with changing the child's nappies.

"She had to teach other kids in the cell to change her diaper," Michelle Brane, from the Women's Refugee Commission, said. The girl - who was four years old - was later reunited with her aunt, but the process took time because she did not speak Spanish but a language indigenous to Guatemala, the agency reports.

"She was so traumatised that she wasn't talking," Ms Brane said, describing the girl. "She was just curled up in a little ball."

She is not alone in voicing concerns over the long-term effects of separating adults and their children.

The American Academy of Pediatrics warned last week that "highly stressful experiences, including family separation, can cause irreparable harm to lifelong development by disrupting a child's brain architecture".

Separately, authorities have announced plans to erect tent cities that will hold hundreds more children in the Texas desert where temperatures regularly reach 40C (105F).

Local lawmaker Jose Rodriguez described the plan as "totally inhumane" and "outrageous", adding: "It should be condemned by anyone who has a moral sense of responsibility."