The controversial policy of separating children from their parents is starting to divide Republicans and their allies as Democrats turn up the pressure.

Former first lady Laura Bush called the policy “cruel” and “immoral”, Republican senator Susan Collins expressed concern about it, and a former adviser to Donald Trump said he thought the issue was going to hurt the president.

Religious groups, including some conservative ones, are also protesting.

Mrs Bush made some of the strongest comments yet about the policy from the Republican side of the aisle.

“I live in a border state. I appreciate the need to enforce and protect our international boundaries, but this zero-tolerance policy is cruel. It is immoral. And it breaks my heart,” she wrote in a guest column for the Washington Post Sunday.

She compared it to the internment of Japanese-Americans during the Second World War, which she called “one of the most shameful episodes in US history”.

Maine senator Ms Collins said she favours tighter border security, but expressed deep concerns about the child separation policy.

“What the administration has decided to do is to separate children from their parents to try to send a message that if you cross the border with children, your children are going to be ripped away from you,” she said.

“That’s traumatising to the children who are innocent victims, and it is contrary to our values in this country.”

Former Trump adviser Anthony Scaramucci said in a weekend interview that the child separation interview could be dangerous for the president, who “should be immediately fixing this problem”.

“This is a fuse that has been lit,” he said. “The president is going to get hurt by this issue if it stays out there very, very long.”

The signs of splintering of Republican support come after a long-time Trump ally, the Rev Franklin Graham, called the policy “disgraceful”.

Numerous religious groups, including some conservative ones, have pushed to stop the practice of separating immigrant children from their parents.

This pressure is coming as White House officials have tried to distance themselves from the policy.

Mr Trump blames Democrats falsely for the situation. The administration put the policy in place and could easily end it after it led to a spike in cases of split and distraught families.

“Nobody likes” breaking up families and “seeing babies ripped from their mothers’ arms”, said presidential counsellor Kellyanne Conway.

Nicole Hernandez holds on to her mother at a border crossing near Tijuana
Nicole Hernandez holds on to her mother at a border crossing near Tijuana (Gregory Bull/AP)

Nearly 2,000 children were separated from their families over a six-week period in April and May after attorney general Jeff Sessions announced a new “zero-tolerance” policy that refers all cases of illegal entry for criminal prosecution.

US protocol prohibits detaining children with their parents because the children are not charged with a crime and the parents are.

Mr Trump plans to meet House Republicans on Tuesday to discuss pending immigration legislation amid an election-season debate over one of his favourite issues.

The House is expected to vote this week on a bill pushed by conservatives that may not have enough support to pass, and a compromise measure with key proposals supported by the president. The White House has said Mr Trump would sign either of those.