Donald Trump’s sister described the US president as cruel and a liar whose lack of principles meant he could not be trusted, according to secretly made recordings published on Saturday.

It was the latest unflattering insider account to target the president – only instead of a jilted aide or business associate, it was from one of his closest relatives.

Maryanne Trump Barry, a former federal judge, reportedly slammed her brother over his immigration policy that saw children separated from their parents at the border and sent to detention centres.

“All he wants to do is appeal to his base,” she said in recordings first reported by The Washington Post and then obtained by The Associated Press.

“He has no principles. None.

“His goddamned tweet and lying, oh my God.”

The recordings were secretly made by the president’s niece Mary Trump, who last month published a bombshell memoir of the “toxic family” that produced him.

The president’s younger brother Robert, who died last week, went to court to try to block its publication, arguing that Mary was violating a non-disclosure agreement signed in 2001 after the settlement of her grandfather’s estate, but to no avail.

About 950,000 copies of Too Much and Never Enough: How My Family Created the World’s Most Dangerous Man were sold on the day of the memoir’s release, with the White House calling it a “book of falsehoods”.

Mary said on Saturday that she made the recordings in 2018 and 2019.

At one point in the recordings, Ms Trump Barry said to her niece: “It’s the phoniness of it all. It’s the phoniness and this cruelty. Donald is cruel.”

The recordings came to light just a day after Robert was memorialised in a service at the White House. Later, the president was dismissive of the recordings.

“Every day it’s something else, who cares. I miss my brother, and I’ll continue to work hard for the American people,” Donald Trump said in a statement.

“Not everyone agrees, but the results are obvious. Our country will soon be stronger than ever before.”

In the weeks since the release of Mary’s tell-all book about her uncle, she has been questioned about the source of some of its information.

Nowhere in the book does she say that she recorded conversations with her aunt.

On Saturday, Mary revealed that she had covertly taped 15 hours of face-to-face conversations with Ms Trump Barry.

“Mary realised members of her family had lied in prior depositions,” said Chris Bastardi, a spokesman for Mary.

“Anticipating litigation, she felt it prudent to tape conversations in order to protect herself.”

In one recording, Ms Trump Barry, 83, said she had heard a 2018 interview with her brother on Fox News in which he suggested that he would put her on the border to oversee cases of immigrant children separated from their parents.

“His base, I mean my God, if you were a religious person, you want to help people. Not do this,” Ms Trump Barry said.

The president has frequently spoken highly of his sister; the recordings are the first time a family member, outside of Mary, has been critical of him.

Mary’s book was filled with attacks on her uncle, including the assertion – which he denied – that he paid someone to take the SATs for him as he sought to transfer into the University of Pennsylvania.

“He got into University of Pennsylvania because he had somebody take the exams,” Ms Trump Barry said, adding she even remembered the man’s name.

In one recording, the federal judge says that a Joe Shapiro took the test for Mr Trump. The president was friends with a person at Penn named Joe Shapiro, who is deceased. Mr Shapiro’s widow and sister said he never took a test for anyone.

Mr Bastardi said of Mary: “She never expected to learn much of what she heard, including the president’s sister, federal judge Maryanne Trump Barry, state that Donald Trump had paid someone to take an SAT exam for him.”

Ms Trump Barry can be heard saying that she guesses that her brother has never read her opinions on immigration cases.

“What has he read?” Mary asks her aunt.

Ms Trump Barry responds: “No. He doesn’t read.”

At another point she says: “I’m talking too freely, but you know. The change of stories. The lack of preparation. The lying. Holy s–t.”