Speaking the day that a court in London blocked the extradition to the US of Julian Assange on medial grounds, Mr Ellsberg said there were several parallels between his case, and the attempted prosecution of the WikiLeaks founder.
In 1971, Mr Ellsberg, working as an analyst for the RAND corporation leaked to to several newspapers, thousands of classified files that came to be known as the Pentagon Papers.
They revealed that contrary to what the government and top military officials said, America knew early on in the conflict with Vietnam, that it could not win. Despite this, the conflict raged on for several further years, claiming in total more than one million lives of North and South Vietnamese soldiers, and 59,000 US troops.
Mr Ellsberg was charged under the Espionage Act, the same piece of 1917 legislation with which the US has indicted Mr Assange. The charges against Mr Ellsberg were thrown out, whereas the US government has appealed Monday’s ruling by a British judge not to permit Mr Assange to be extradited as it was likely he may try to take his life.
Speaking at a virtual event organised by the Courage Foundation, which supports whistleblowers, and joined by Noam Chomsky and lawyer Marjorie Cohen, Mr Ellsberg said he regretted not leaking the material the moment he found it, and waiting several years as he became increasingly disillusioned with the US authorities, and defence secretary Robert McNamara.
“I believe, I have very little doubt, there is highly classified planning going on to provoke an Iranian action, a response to our provocation, that will give a pretext to launch an attack as [Donald Trump] has wanted to do for years,” he said.
“He has 17 or 18 days left to do that. More than enough time. It's also enough time to block him by an informed public, if that information got out.”
He said he believed the information existed in files that were marked covert or top secret. “I think people who have access to that, I would encourage, I do encourage you to share that information, not only with the Congress, especially the House, and for press, so that we have a chance of avoiding that [conflict].”
During his presidency, Mr Trump pulled the US from the Iran Nuclear and reimposed sanctions on Iran, as it sought to impose pressure on Tehran. Washington also launched a propaganda campaign against the Iranian government, and the US president has routinely threatened it.
“Upon information and belief, Iran or its proxies are planning a sneak attack on US troops and/or assets in Iraq,” Mr Trump tweeted last April. “If this happens, Iran will pay a very heavy price, indeed!”
Mr Ellsberg did not provide any evidence to back his claim the US might be seeking to provoke Iran. Yet, this was not the first time he has urged people in possession of secret information that could save lives, to make it public.
Two years ago in an interview with The Independent that coincided with the release of the movie The Post, he spoke in similar terms.
The movie told the story of the Washington Post’s fight to publish the material he leaked, and Mr Ellsberg was portrayed by Matthew Rhys.
“I was not interested in history. I wanted to enlighten people right then,” Mr Ellsberg said. “The analogy to now is the same. We’re involved in wars in Iraq and Afghanistan. I would hope someone would put out the information in the media now.”
On Monday, the veteran whistleblower and peace activist, said he was the department of justice would consider the leaking of such material equivalent to “what they’re charging Julian Assange with”.
“I think it would be highest act of patriotism,” he said. “The opposite of treason, and very much in the interest of not only the United States, or Iran and the Middle East, but the world as a whole.”
He said: “I'm talking about the next couple of weeks. So I would say to people, do it right now. Don't do what I did. Don't wait years after the bombs have started falling. Put this information out…today, this week or next week. Not a month from now when it could well be too late.”