One of Donald Trump's former top campaign advisers has pleaded guilty to lying to the FBI during investigations into possible collusion between the Trump campaign and Russia.

George Papadopolous, 30, pleaded guilty to the charges earlier in the month but the revelation has just been made by the special counsel heading up the investigation.

It comes just hours after Trump's former campaign chairman and an associate were charged on 12 counts including conspiracy against the US.

The sealed document which was released today (30 October), revealed that Papadopolous did "willfully and knowingly make a materially false, fictitious and fraudulent statement" in which he lied to special agents about "the timing, extent and nature of his relationship and interactions with foreign nationals whom he understood to have close connections with senior Russian government officials."

Reacting before the latest bombshell, Trump reacted to the Manafort charges, re-emphasising his own thoughts that there has been "no collusion."

Over two tweets, the president said: "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?????

"Also, there is NO COLLUSION!"

The White House has remained adamant that despite the ongoing investigation, former FBI director Robert Mueller would remain at the head of the investigation.

The senate minority leader Chuck Schumer issued a warning shot to Trump against any form of interference with the investigation, saying that Mueller's probe should continue "unimpeded."

"The President must not, under any circumstances, interfere with the special counsel's work in any way. If he does so, Congress must respond swiftly, unequivocally, and in a bipartisan way to ensure that the investigation continues," Schumer said in a statement.