Pentagon Papers whistleblower Daniel Ellsberg urges James Mattis to protect world from Donald Trump

An AFP file photo dating from 2013 shows Pentagon Papers whistleblower Daniel Ellsberg at a demonstration at Fort Meade, Maryland.

Famous US whistleblower Daniel Ellsberg, who leaked the Pentagon Papers in 1971, has called on Pentagon chief James Mattis to "protect us" from US President Donald Trump by resisting orders to launch military actions or use nuclear weapons.

"The situation is closer to the possible use of nuclear weapons since any time I would say in 50 years," Ellsberg told AFP in a telephone interview on Friday.

"It is a very dangerous time," Ellsberg said, shortly before the news broke on Saturday that the United States, Britain and France -- three nuclear powers -- were carrying out missile strikes against Syria.

Western military actions in Syria, involving four nuclear-armed states, coupled with the political pressures on Trump at home could easily spell disaster, Ellsberg warned.

Ellsberg, a former military analyst and nuclear war planner turned world-famous whistleblower, pointed out that Trump's war of words with North Korea was the first time since the Cuban missile crisis in 1962 that a US president has threatened military action against another nuclear-armed state.

He said Trump has a strong desire to launch a war as a form of distraction from the US government probe led by Justice Department special prosecutor Robert Mueller investigating Trump’s alleged election campaign ties to Russia.

"The president I'm afraid has a very strong temptation to start a war as cover for his firing the special prosecutor," he said.

Ellsberg famously leaked thousands of documents nearly 50 ago revealing that successive US administrations had lied to the American public about escalating the Vietnam War.

The 87-year-old pointed out that under former President Richard Nixon, then Pentagon chief James Schlesinger had secretly insisted that no orders from Nixon to launch military action or use nuclear weapons should be obeyed unless he approved the orders.

“Now that is an unconstitutional order, and it would be unconstitutional for James Mattis to make such a directive right now. Nevertheless, he ought to do it... We are depending on 'Mad dog Mattis' to protect us from a president," he said.

Ellsberg said there was a desperate need for high-level people like Mattis and General Joseph Dunford, the highest-ranking officer in the US military, to be willing "to put their careers on the line" to do the right thing and help avert catastrophe.

"I think Mattis in particular, and Dunford, are cooling the president down from his threats of a catastrophic action in North Korea and even in Syria," he said.

He insisted that without a declaration of war by Congress or a UN Security Council directive, any order to go to war "would be a criminal order and they should not obey it."

Ellsberg is a staunch anti-nuclear weapons campaigner who recently published a massive article titled "The Doomsday Machine: Confessions of a Nuclear War Planner."

"I think people really are worried about Trump being the person who has his finger on what he calls his very big nuclear button. It doesn't reassure anybody," he said.