Germany's ambassador to the United States has warned that the incoming Trump administration will rob U.S. law enforcement and the media of their independence and hand big tech companies "co-governing power", according to a confidential document seen by Reuters.

The briefing document, dated Jan. 14 and signed by Ambassador Andreas Michaelis, describes Donald Trump's agenda for his second White House term as one of "maximum disruption" that will bring about "a redefinition of the constitutional order - maximum concentration of power with the president at the expense of Congress and the federal states."

"Basic democratic principles and checks and balances will be largely undermined, the legislature, law enforcement and media will be robbed of their independence and misused as a political arm, Big Tech will be given co-governing power," it says.

Trump's transition team had no immediate comment on the ambassador's assessment.

On Sunday, German Foreign Minister Annalena Baerbock said Berlin would "continue to work closely together [with the U.S.], but of course we also want to continue to stand up for our own interests."

Asked to explain the ambassador's stance on Trump on German public broadcaster ZDF, Baerbock said Michaelis was merely doing his job and that Trump had openly stated much of his agenda.

The outgoing government of Chancellor Olaf Scholz has largely refrained from direct public criticism of Trump since the election, but the ambassador's confidential assessment offers a blunt view from a senior German official.

Ambassadors are not replaced automatically with the formation of a new government, unless a change is deemed necessary for diplomatic or other reasons.

The document cites the judiciary, and especially the U.S. Supreme Court, as central to Trump's attempts to further his agenda, but says that despite the court's recent decision to expand presidential powers, "even the biggest critics assume that it will prevent the worst from happening."

Michaelis sees control of the Justice Department and FBI as key to Trump reaching his political and personal goals, including mass deportations, retribution against perceived enemies and legal impunity.

He says Trump has broad legal options to force his agenda on the states, saying "even military deployment within the country for police activities would be possible in the event of declared 'insurrection' and 'invasion'."

The 1878 Posse Comitatus Act bars the federal military from participating in domestic law enforcement, with some exceptions.

Michaelis also foresees a "redefinition of the First Amendment," saying Trump and billionaire X owner Elon Musk are already taking action against critics and non-cooperating media companies.

"One is using lawsuits, threatening criminal prosecution and licence revocation, the other is having algorithms manipulated and accounts blocked," he says in the document.

Musk's repeated endorsement of the far-right Alternative for Germany (AfD) ahead of the Feb. 23 national election has drawn ire in Berlin, but the government has stopped short of unanimously leaving his platform.

Berlin endured a particularly difficult relationship with the United States during the first Trump administration, facing costly tariffs and criticism over its failure to meet the NATO target on defence expenditure.