Paul Manafort, the former chairman of the campaign to elect Donald Trump as President, has been formally charged with conspiring against the United States, money laundering and making false statements.

The charges against Manafort and his business partner and fellow Trump campaign worker, Rick Gates, are the first laid by Special Counsel Robert Mueller as part of his investigation into possible collusion between the Trump campaign and Russia during last year’s US election.

Manafort and Gates surrendered separately to the FBI first thing Monday morning (US time). The pair have pleaded not guilty to a dozen serious charges.

The pair were confined to house arrest and bond was set at $US10 million ($A13 million) for Manafort and $US5 million ($A6.5 million) for Gates. They will next appear before court on Thursday local time.

Their charges include conspiracy to launder money, being an unregistered agent of a foreign principal, false and misleading statements and seven counts of failure to file reports of foreign bank and financial accounts.

A White House spokeswoman said the indictment had nothing to do with Trump or his campaign and showed no evidence of collusion between the campaign and Russia.

“Today’s announcement has nothing to do with the President, has nothing to do with the President’s campaign or campaign activity,” White House spokeswoman Sarah Huckabee Sanders said.

“The real collusion scandal has everything to do with the Clinton campaign.

“We’ve been saying from day one there’s no evidence of Trump-Russia collusion, and nothing in the indictment today changes that at all.”

Meanwhile, in a separate bombshell development, one of the Trump campaign’s foreign policy advisers admitted he met a Russian contact to discuss email “dirt” on Hillary Clinton after first denying it.

The former adviser, George Papadopoulos, lied when he told authorities in January that he’d met a Russian professor with substantial government connections before he began advising the Trump campaign.

In fact, he met him just days after he signed on and he has now admitted that.

Reports say Mr Papadopoulos tried to arrange a meeting between the Trump campaign and Russian officials. Photo: Twitter/CNN

The New York Times called Papadopoulos’s admission “the most explicit evidence connecting the Trump campaign to the Russian government’s meddling in last year’s election”.

Court documents show Papadopoulos repeatedly tried to arrange a meeting between the Trump campaign and Russian government officials, according to the paper.

President Trump, who’d spent much of the weekend in a Twitter fury demanding action against Hillary Clinton, continued that theme Monday morning as Manafort and Gates turned themselves in and Papadopoulos’s guilty plea emerged.

“Sorry, but this was years ago, before Paul Manafort was part of the Trump camapaign,” the president tweeted soon after the indictments were made public. “But why aren’t Crooked Hillary & the Dems the focus?????”

He followed up just three minutes later with: “… Also, there is NO COLLUSION!”

Special counsel Mueller said Manafort laundered more than $18 million to buy properties and services. He’s alleged to have funnelled millions through overseas shell companies and used the money to buy luxury cars, real estate and antiques.

“Manafort used his hidden overseas wealth to enjoy a lavish lifestyle in the United States without paying taxes on that income,” the indictment alleges.”

Sorry, but this is years ago, before Paul Manafort was part of the Trump campaign. But why aren't Crooked Hillary & the Dems the focus?????

— Donald J. Trump (@realDonaldTrump) October 30, 2017

….Also, there is NO COLLUSION!

— Donald J. Trump (@realDonaldTrump) October 30, 2017

Gates is accused of transferring more than $3 million from offshore accounts. Both are facing charges of making false statements.

Mueller was appointed in May this year to oversee the probe of possible coordination between the Trump campaign and Russia, following Trump’s sacking of former FBI Director, James Comey, who had overseen the investigation since July 2016.

Trump initially claimed he sacked Comey because of his handling of the FBI’s investigation of the so-called Hillary Clinton email scandal in the run up to last year’s election. He admitted in a later interview though it was because of the Russia investigation.

The Washington Post reported today that Mueller’s interest in Manafort dates back to at least 2014, long before he was directly connected to the Trump campaign.

Prosecutors have been looking into Manafort’s work as a political consultant in Ukraine, where he advised a Russia-friendly political party for years before his work with Trump.

Whatever the outcome of today’s charges, they increase pressure on Manafort and Gates and potentially others to review their evidence or cooperation with the Mueller investigation.

Manafort, a veteran Republican Party strategist, joined the Trump campaign in March 2016 and was soon promoted to chairman and chief strategist. But just months later Mr Trump fired him.

He’d been linked to secret payments of millions and to a prominent Ukraine politician with pro-Russia sympathies, Viktor Yanukovych.

Manafort had been seen walking into the FBI’s Washington Field Office Monday morning after a weekend of intense media speculation here that charges were imminent.

This, in turn, prompted a wave of anti-Mueller sentiment from Mr Trump and his key media outlets, most prominently the Murdoch-owned Fox News, Wall Street Journal and New York Post.

They each tried their hardest to shift the focus off last year’s victorious Trump campaign and onto Mrs Clinton’s unsuccessful one and called for Mr Mueller’s removal or resignation.

This led to speculation that Mr Trump might move to sack Mr Mueller, as he did Mr Comey.

CNN reported today that Mr Trump “remains furious” at the widening Mueller investigation but he has been persuaded to not renew his call to fire the special counsel.

FBI agents raided Manafort’s home earlier this year, searching for tax and international banking records.

Manafort has been the subject of a longstanding FBI investigation into his dealings in Ukraine and work for the country’s former president, Mr Yanukovych. That investigation was incorporated into Mr Mueller’s broader probe.

In Gates, Mr Mueller brings in not just Manafort’s chief deputy, but a key player from Trump’s campaign who survived Manafort’s sacking last summer.

As of two weeks ago, Gates was still working for Tom Barrack, a Trump confidant, helping with the inauguration committee’s campaign account.

– with Agencies