Peter Ricketts said Canberra's decision to abandon a contract with Paris for diesel-powered subs in favour of nuclear-powered ones from Washington drove a wedge between the allies and weakened the transatlantic alliance.

"I think this move certainly undermines French confidence in NATO and NATO allies, and therefore reinforces their feeling that they should be driving for European strategic autonomy," he told AFP.

"I think that can only be damaging to NATO, because NATO depends on trust. The repair work needs to begin urgently."

EU foreign ministers are due to discuss the new defence pact signed between the United States, Australia and Britain, on the sidelines of the UN General Assembly Monday.

The deal -- dubbed AUSUK -- was announced last week, prompting France to claim it had been "stabbed in the back" by Australia and triggering an angry war of words.

- A 'turning point' in relations -

Ricketts, Britain's top diplomat in Paris between 2012 and 2015, likened the dispute to French opposition to US president George W. Bush's pursuit of war in Iraq.

France's president at the time, Jacques Chirac, warned against the conflict to oust Saddam Hussein, which Britain, led by prime minister Tony Blair, backed.

"It (the submarine deal) will be remembered in France, I'm sure, like the rift over Iraq in 2003, and things won't be quite the same," said Ricketts.

"I think it will tend to reinforce the feeling among Europeans that America is now a less reliable ally than it was," he added.

Ricketts, who was permanent representative to NATO in 2003-2006, said France would view the row as "a turning point" in relations with the United States and Britain.

"It's reinforced a feeling in Paris that I pick up that the Americans are increasingly turning their back on European security allies and focusing on their confrontation with China," he added.

"And that Britain, by this move, is following in the same direction."

Britain's Prime Minister Boris Johnson has sought to downplay any effects on its relations with France, insisting it remained one of its closest military allies.

But France's Foreign Minister Jean-Yves Le Drian accused London, which has recentred its foreign policy on the Indo-Pacific region post-Brexit, of "constant opportunism".

video-phz/csp/jj