The White House has said it was "not an order" when US President Donald Trump called for his Attorney-General to end special counsel Robert Mueller's probe of Russia's election intervention.

Key points: US press secretary says Mr Trump's calls to end investigation is the President "fighting back"

US press secretary says Mr Trump's calls to end investigation is the President "fighting back" Mr Trump suggests Paul Manafort being treated worse than Al Capone

Mr Trump suggests Paul Manafort being treated worse than Al Capone Mr Manafort is in detention after having his bail revoked on allegations of witness tampering

Taking to Twitter to complain about the federal Russia investigation, which focuses on the 2016 presidential campaign, Mr Trump said Attorney-General Jeff Sessions "should stop this Rigged Witch Hunt right now, before it continues to stain our country any further".

Some Democratic politicians said Mr Trump's tweets showed an intent to obstruct justice, by ordering Mr Sessions to stop the investigation.

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But White House press secretary Sarah Sanders said Mr Trump's comments were simply the President "fighting back".

"The President is stating his opinion — it's not an order," Ms Sanders said.

"There is a reason that the President is angry and frankly most of America is angry as well.

"And there is no reason he shouldn't be able to voice that opinion."

Mr Trump's lawyer Rudy Giuliani also backed the President's call to end the investigation.

"I said it about two weeks ago … we believe that the investigation should be brought to a close," Mr Giuliani said in New Hampshire.

"I guess, if we were playing poker — we're not — put up or shut up, what do you got?"

Trump distances himself from Manafort

This courtroom sketch depicts Paul Manafort, seated right row second from right, together with his lawyers. ( AP: Dana Verkouteren )

Tuesday marked the first day of Paul Manafort's trial on charges of tax evasion and bank fraud brought by Mr Mueller's team, charges that stemmed from Mr Manafort's consulting work for Ukraine, for which he allegedly received millions he did not report to the US government.

Seeking to distance himself from his ex-campaign chairman, Mr Trump tweeted: "He worked for me for a very short time."

Mr Manafort's involvement in the Trump campaign spanned six months, and he helped lead efforts to secure the GOP nomination for Mr Trump in 2016.

Mr Manafort's involvement in the Trump campaign spanned six months. ( Reuters: Rick Wilking )

In a separate tweet, Mr Trump asked whether his former top political aide was being treated worse than Al Capone, tweeting Mr Manafort was "now serving solitary confinement — although convicted of nothing?"

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Al Capone, the infamous gangster, was convicted of tax evasion and served most of the 1930s in prison before being paroled.

Mr Manafort is in detention after having his bail revoked because of allegations he was attempting to tamper with witnesses in his case.

Federal prosecutors revealed last month that he was afforded unusual privileges while in detention.

Sorry, this video has expired Paul Manafort's lawyer arrives at court to begin trial

Mr Trump said the charges against Mr Manafort "have nothing to do with Collusion".

Potential coordination between Russian government agents and the Trump campaign is still a matter of investigation by Mr Mueller's team, which is also investigating potential obstruction of justice by the President.

Mr Trump called any talk of collusion "a Hoax".

'Not on trial for having a lavish lifestyle'

Protesters gathered outside the courthouse in Alexandria, Virginia. ( AP: Manuel Balce Ceneta )

Mr Manafort's consulting work for pro-Russian politicians in Ukraine that earned him $60 million took the spotlight on the second day of testimony in federal court.

The judge tried to rein in prosecutors in their description of Mr Manafort's lavish lifestyle.

With the jury out of the room, US District Judge TS Ellis complained about prosecutors' efforts to show that Mr Manafort's life was luxurious and blocked them from showing one document on home renovations.

"Mr Manafort is not on trial for having a lavish lifestyle," Mr Ellis said.

At one point, Mr Ellis even called out lawyers from both sides for rolling their eyes.

"Let's move it along," Mr Ellis said repeatedly.

Prosecutors have portrayed Mr Manafort as a tax cheat who hid money in offshore accounts, and lied to borrow millions more against real estate in a bid to maintain an extravagant lifestyle once the work dried up.

Mr Manafort, 69, has pleaded not guilty to all charges.

Paul Manafort (fourth from R) stands with his lawyers before opening statements. ( AP: Dana Verkouteren )

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