Former Trump campaign chairman Paul Manafort and his associate Rick Gates have been indicted by a federal grand jury Monday on 12 counts, according to the special counsel’s office.

The special counsel’s office told Fox News that the counts include conspiracy against the United States, conspiracy to launder money, unregistered agent of a foreign principal, false and misleading Foreign Agent Registration (FARA) statements, false statements and seven counts of failure to file reports of foreign banks and financial accounts.

Manafort and Gates will appear before Magistrate Judge Deborah Robinsonat 1:30pm on Monday for an initial appearance and arraignment, the special counsel's office said.

In addition, a guilty plea by former Trump campaign policy adviser George Papadopoulos was announced by Mueller. He admitted to making false statements to FBI agents as part of the investigation.

The cases were unsealed Monday, after Manafort and Gates were permitted to surrender themselves to the custody of the FBI, the special counsel’s office told Fox News.

Paul Manafort, who was indicted on 12 counts by a federal grand jury, served as Trump's campaign chairman. This photo was taken in July 2016 at the Republican National Convention in Cleveland, Ohio. (AP)

Manafort and Gates face the first charges in the special counsel’s investigation. This is also the first time the special counsel's office has confirmed that a grand jury has been impaneled.

President Trump tweeted on the news of the indictments.

An error occurred while retrieving the Tweet. It might have been deleted.

"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?????" Trump tweeted, adding moments later, "....Also, there is NO COLLUSION!"

According to the indictment, reviewed by Fox News, between at least 2006 and 2015, Manafort and Gates acted as unregistered agents of the Government of Ukraine, the Party of Regions, a Ukrainian political party whose leader Victor Yanukovych was president from 2010 to 2014, and the Opposition Bloc. Manafort and Gates generated tens of millions of dollars in income as a result of their work in Ukraine.

The indictment says that Manafort and Gates laundered the money through scores of the United States and foreign corporations, partnerships and bank accounts in order to hide Ukraine payments from U.S. authorities.

More than $75 million flowed through offshore accounts. Manafort, alone, laundered more than $18 million which was used by the former Trump campaign chairman to buy property, goods, and services in the U.S. Manafort concealed that income from the U.S. Treasury and the Department of Justice.

Special Counsel Robert Mueller announced first indictments in Russia probe on Monday. (AP)

First reported by The New York Times, Manafort and Gates are expected in federal court on Monday. Gates is a longtime associate of Manafort. According to The Times, his name appeared on documents linked to companies that Manafort’s firm created in Cyprus to receive payments from politicians and businesspeople in Eastern Europe.

White House lawyer Ty Cobb told Fox News he had no comment on the report at this time.

It was widely speculated that Manafort would receive the first charges in Special Counsel Robert Mueller’s investigation.

Manafort was fired as Trump’s campaign chairman in August 2016, and has been investigated for his dealings in Ukraine several years ago, for which he did not register as a foreign agent until June 2017.

Chairman of the Democratic National Committee, Tom Perez, said the indictment "underscores the seriousness" of the Mueller probe.

"The Chairman of Donald Trump’s campaign and his deputy have been charged with conspiracy against the United States, money laundering, and making false statements – all related to their work to promote a pro-Putin regime," Perez said in a statement. "It’s time for Republicans to commit to protecting this investigation and preserving the rule of law."

But Rep. Pete King, R-N.Y., said on "America's Newsroom" that there is "no evidence" linking the Trump campaign to collusion.

"This pre-dates the campaign entirely, and could pre-date Paul Manafort even meeting Donald Trump. This has nothing to do with the campaign," King told Fox News. "The investigation still has to go forward but what I’ve seen so far, is there is no evidence at all linking the trump campaign to Russian influence or collusion."