The ruling by US Magistrate Judge William Porter said the materials seized from reporter Hannah Natanson could not be reviewed due to pending litigation over the search of her home.

"The government must preserve but must not review any of the materials that law enforcement seized...until the Court authorizes review of the materials by further order," Porter wrote in the ruling.

Natanson, who reports on the US federal government, covered job cuts in Washington after President Donald Trump took office at the start of his second term.

The newspaper reported Natanson's work laptop had been seized during a raid on January 14 at her home in Virginia, along with her personal laptop, cell phone and watch.

US Attorney General Pam Bondi said the search was part of an investigation into an alleged leak from the Pentagon, which has tightened media restrictions since Trump took office.

FBI agents told Natanson she is not the focus of the government probe, but critics say the move could set a dangerous precedent chilling US press freedom.

A statement from The Washington Post said the seizure of their reporter's "confidential newsgathering materials chills speech, cripples reporting, and inflicts irreparable harm every day the government keeps its hands on these materials."

"We have asked the court to order the immediate return of all seized materials and prevent their use," the statement continued. "Anything less would license future newsroom raids and normalize censorship by search warrant."