President Donald Trump has lashed out against special counsel Robert Mueller's Russia investigation, branding it "an attack on our country" and exhibiting mounting concern about the year-long probe after federal authorities raided the offices of his personal lawyer.
Caught off guard and furious with the inquiry, the president showed a flare of temper watching cable news coverage of the raid on Monday afternoon, summoning lawyers Ty Cobb and Jay Sekulow to get their opinion of what was happening.
Aides and outside allies described Trump as shaken and increasingly frustrated by the development, and they said his reaction had sparked discussion about whether the raid would usher an unpredictable new phase in how the president responds to the probe.
Trump vented from the Oval Office that Mueller's investigators were "going too far" and conducting "their witch hunt" to undermine his presidency, according to three people familiar with the president's views but not allowed to discuss them publicly.
Minutes later he publicly unleashed his sharpest invective to date against the sweeping investigation, calling the Monday search "a disgrace."
"It's an attack on our country in a true sense," he said in the Cabinet Room, flanked by the nation's top military brass, who watched the scene stone-faced. "It's an attack on what we all stand for."
Trump let loose after federal agents pierced the protective bubble around him, seizing records from the offices of longtime Trump lawyer Michael Cohen, on topics including a $US130,000 ($A169,000) payment made to a porn actress who says she had sex with Trump more than a decade ago.
Cohen claims to have used a personal home equity loan to pay the adult film actress, known as Stormy Daniels.
The president didn't bat away the idea of firing Mueller, saying people have advised him to take that action: "Why don't I just fire Mueller? Well, I think it's a disgrace what's going on - we'll see what happens."
Trump called the probe a "witch hunt," complaining it distracts from serious issues such as consideration of a military response to the apparent use of a chemical weapon on Syrian civilians over the weekend.
With reporters in the Cabinet Room and cameras rolling on Monday evening, Trump opened with a four-minute critique of Mueller's investigation.
"I just heard that they broke into the office of one of my personal attorneys, a good man," Trump began, referring to agents who had obtained search warrants from a federal judge.
Mueller, a lifelong Republican, and his team of attorneys have been investigating Russian interference in the 2016 election and associated misdeeds in the president's orbit since May 2017.
Senate Democratic leader Chuck Schumer of New York released a statement warning Trump against firing Mueller. "The investigation is critical to the health of our democracy and must be allowed to continue," he said.
