The Kremlin leader is "very rational" and "knows what he's doing", said the former Swedish foreign minister, who repeatedly insisted that Iraq was not developing nuclear weapons before the Gulf War of 1990.

Blix, 96, who headed the International Atomic Energy Agency (IAEA) from 1981 to 1997, spoke to AFP on a range of issues in an hour-long interview at his apartment in central Stockholm.

Blix later headed a team of UN inspectors tasked with determining whether Saddam Hussein had weapons of mass destruction.

He was never able to confirm that.

His findings contradicted claims made by US president George W. Bush, who ordered the invasion of Iraq in 2003.

"It was a terrible mistake on the part of the US, based on erroneous information and a hubris that the US intelligence knew better than what we did," Blix told AFP. "The Iraq War was an aberration."

At the time, the US was not at risk of Russia or China intervening, Blix said, and the US and Britain took it upon themselves "to be the world's sheriffs".

Blix is today more optimistic about the future of global conflicts.

- Putin made a 'mistake' -

The former diplomat last year published a book called "A Farewell to Wars" -- a title he admitted was "very provocative" given the "headwind right now", with wars raging in Ukraine and Gaza.

Like the US invasion of Iraq, Blix called Russia's invasion of Ukraine an "aberration".

"Putin committed a mistake, and I'm sure he regrets it," he said.

The IAEA warned on August 17 that the safety situation at the Zaporizhzhia nuclear power plant was "deteriorating" following a nearby drone strike.

The plant, which was seized by Russia's forces early in the war, has come under repeated attacks that both sides have accused each other of carrying out.

But Blix, who headed the IAEA during the 1986 Chernobyl disaster, doesn't think Russia would attack the site on purpose.

"I don't think the Russians would do it deliberately, no."

"I would be very surprised if the Russians had not instructed their military to stay away from severe damage."

And he isn't concerned either about Putin's repeated threats to the West of nuclear warfare.

"He scrambles, he shakes the nuclear weapons and threatens, but he is no fool."

"As long as there exists the possibility of a second strike, there is the fear of escalation."

"The big powers -- the US and Russia and China -- don't want to get into a situation of direct confrontation with each other."

Looking ahead to a future after the war in Ukraine, Russia will eventually "have to come back to the world and to Europe", Blix said, though "it will take time".

"Maybe," he said, "there will also be a feeling that now we have to somehow patch up and improve the situation."

"I'm a multilateralist," he said, smiling.

"There are so many problems in the globalising world that you cannot manage (if you are) isolated."

Blix said the international community needed to work together to tackle its biggest challenges, including global warming -- which he was "more worried" about than the spectre of war -- as well as pandemics and the fight against international organised crime.