A US judge has temporarily blocked publication of a book by President Donald Trump's niece Mary while he considers whether the tell-all represents a violation of a confidentiality agreement among family members.

The book, Too Much and Never Enough: How My Family Created the World's Most Dangerous Man, has been marketed as a rare look into the "inner workings" of the "toxic" Trump family.

According to court papers, Mary Trump will reveal herself to be the source for an explosive New York Times report on Trump's taxes.

The freeze is in effect only while the judge, Hal Greenwald, considers the case. Both sides have to have submitted their legal arguments by July 10. The publication of the book was scheduled for July 28.

Mary Trump's lawyer, Ted Boutrous, was not ready to give up on the publication of the book as originally scheduled.

"The trial court's temporary restraining order is only temporary, but it still is a prior restraint on core political speech that flatly violates the First Amendment. We will immediately appeal. This book, which addresses matters of great public concern and importance about a sitting president in an election year, should not be suppressed even for one day," Boutrous said.

Robert Trump, the president's younger brother, filed a lawsuit last week in Dutchess County Supreme Court to block the book.

"The actions of Mary Trump and Simon & Schuster are truly reprehensible. We look forward to vigorously litigating this case, and will seek the maximum remedies available by law for the enormous damages caused by Mary Trump's breach of contract and Simon & Schuster's intentional interference with that contract," Robert Trump's lawyer Charles Harder said. "Short of corrective action to immediately cease their egregious conduct, we will pursue this case to the very end."

Harder has represented the president in legal battles with the press.

Robert Trump initially sued in Queens Surrogate's Court, where the family's confidentiality agreement was filed. He then refiled in Dutchess County, where he lives.

Australian Associated Press