The US Justice Department is investigating whether there was a secret scheme to lobby White House officials for a pardon as well as a related plot to offer a hefty political contribution in exchange for clemency, according to a court document unsealed on Tuesday.

Most of the information in the 18-page court order is redacted, including the identity of the people prosecutors are investigating, and for whom the proposed pardon might be intended.

But the document from August does reveal people are suspected of having acted to secretly lobby White House officials to secure a pardon or sentence commutation and that, in a related scheme, a substantial political contribution was floated in exchange for a pardon.

As part of the investigation, more than 50 laptops, iPads and other digital devices have been seized, according to the document.

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President Donald Trump, who last week pardoned his first national security adviser, Michael Flynn (Patrick Semansky/AP)

The existence of the investigation was revealed in a court order from US District Judge Beryl Howell, the chief judge of Washington’s federal court, in which she granted investigators access to certain email communications connected to the alleged schemes that she said was not protected by attorney-client privilege.

Prosecutors will be able to use that material to confront any subject or target of the investigation, the judge wrote.

The order was dated August 28, and prosecutors sought to keep it private because they said it identified people not charged by a grand jury. But on Tuesday, Ms Howell unsealed that document while redacting from view any personally identifiable information.

President Donald Trump tweeted Tuesday night: “Pardon investigation is Fake News!”

Pardons are common at the end of a president’s tenure and are occasionally politically fraught affairs as some convicted felons look to leverage connections inside the White House to secure clemency.

Last week, Mr Trump announced he had pardoned his first national security adviser, Michael Flynn, even as a federal judge was weighing a Justice Department request to dismiss the case.

A Justice Department official said on Tuesday night that no government official was or is a subject or target of the investigation, first reported by CNN.