Special Counsel Robert Mueller wants to see witness' personal phone so he can examine their encrypted conversations as he investigates Russia's role in the 2016 election.

The request could potentially let him see conversations between close associates of President Donald Trump as the special counsel examines whether or not the president obstructed his investigation.

Since at least April, Mueller's team has demanded witness' phones so they can examine private conversations on encrypted apps like WhatsApp, Confide, Signal and Dust, sources told CNBC.

Special counsel Robert Mueller is looking for conversations that weren't previously disclosed

Mueller's request could reveal to investigators conversations with those close to Trump

Paul Manafort reportedly used WhatsApp to talk to witnesses in his case

The witness have done so out of fear they will be subpoenaed if they don't.

It's unknown if the demand has resulted in new information for the investigative team but they seem to think the apps will expose conversations that weren't previously disclosed.

The apps are designed to keep conversations private.

The revelations about Mueller's new demand comes as the special counsel wants Trump's former campaign manager Paul Manafort to be put in jail while he awaits trial because he allegedly tampered with witnesses via encrypted apps.

Mueller filed a motion in federal court asking a judge to revoke Manafort's $10 million bail, The New York Times reported.

Prosecutors working with Mueller say that Manafort tried to contact witnesses in the case using an encrypted messaging program on his cell phone.

Manafort allegedly sent numerous text messages to a potential witness using WhatsApp.

The messages allegedly sent on WhatsApp were then backed up on Manafort's iCloud, according to prosecutors.

Mueller is now asking a judge to either revise the terms of his release or revoke it entirely, which could mean he will have to stay in jail until his trial.

FBI Special Agent Brock Domin, in a declaration filed with Mueller's motion, said Manafort had attempted to call, text and send encrypted messages in February to two people from The Hapsburg Group, a firm he worked with to promote the interests of Ukraine.

The FBI has documents and statements from the two people, as well as telephone records and documents recovered through a search of Manafort's iCloud account showing that Trump's former campaign manager attempted communication while he was out on bail, according to Domin.

The communications were 'in an effort to influence their testimony and to otherwise conceal evidence,' Domin wrote.

'The investigation into this matter is ongoing.'

Manafort is the most senior member of Trump's campaign to be indicted, though the charges do not relate to campaign activities.

He has been indicted for financial crimes related to his work as a lobbyist for foreign actors, which he did not register for until his work was revealed during the campaign.

Trump has denied collusion with Russia and called Mueller's investigation a 'witch hunt.'

Manfort's legal team has also denied any wrong doing.

And Dust was the app reportedly used between longtime Trump personal attorney Michael Cohen and Felix Sater, a real estate developer with ties to Russian when they tried to complete Trump Tower Moscow. The plan ultimately fell apart.