President Barack Obama defended his choice to commute the sentence of Wikileaks whistleblower, Chelsea Manning, but made it clear that he did not issue a pardon.

"Chelsea Manning has served a tough prison sentence," the outgoing President told reporters in his final press conference. "So the notion that the average person who was thinking about disclosing vital classified information would think that it goes unpunished, I don't think would get that impression from the sentence that Chelsea Manning has served."

Mr Obama explained that Ms Manning faced trial and took responsibility for her actions in leaking hundreds of thousands of classified materials in 2010. But he added: "The sentence that she received was very disproportionate to what other leakers had received, and... she had serve a significant amount of time that it made sense to commute and not pardon her sentence."

The White House announced the commutation of the whistleblower's 35-year sentence on Tuesday. She was included in a list of 209 commutations and 64 pardons.

She had spent almost seven years in prison – a large portion of which was spent in solitary confinement in Fort Leavenworth, Kansas, prison.

Republican House Speaker Paul Ryan denounced Mr Obama's decision to grant clemency to Ms Manning shortly after the announcement.

"This is just outrageous," he said. "Chelsea Manning's treachery put American lives at risk and exposed some of our nation's most sensitive secrets.

"President Obama now leaves in place a dangerous precedent that those who compromise our national security won't be held accountable for their crimes."

But Mr Obama said he felt that justice had been served and encouraged whistleblowers who wish to expose wrongdoing to do so through official channels.

"I feel very comfortable that justice has been served and that a message has still been sent that when it comes to our national security," he said, "that wherever possible we need folks who may have legitimate concerns about the actions of the government, their superiors, or the agencies in which they work, that they try to work through the established channels and avail themselves to the whistleblower protections that have been put in place." Ms Manning is set for release 17 May 2017.

On Wednesday lawyers for Julian Assange said US officials had not met the WikiLeaks founder's conditions for agreeing to be extradited to the United States. Last week Mr Assange offered not to fight extradition if Chelsea Manning were offered clemency. His lawyers now say he was demanding that Manning be freed "immediately".