It's a golden rule of politics: always assume the microphone is on.

But as many world leaders can testify, it's a rule that's often forgotten.

'Hot mic' moments have heaped embarrassment on politicians across the globe, from America to Australia.

Just this week, Canadian Prime Minister Justin Trudeau was caught appearing to mock US President Donald Trump at a Nato meeting.

Unguarded comments like these have been a source of humiliation, sometimes with huge political fallout.

They have also shone a light into the murky corridors of international diplomacy - for better or worse. Here are five of the most memorable.

1. Ronald Reagan: 'We begin bombing in five minutes' (1984)

Image caption US President Ronald Reagan was often known to crack jokes during sound checks

At the height of the Cold War, US President Ronald Reagan turned up the diplomatic heat with a riff on Soviet Russia.

During a soundcheck before his weekly radio address, Mr Reagan joked with sound engineers who were recording him for NPR radio.

"My fellow Americans," the president said. "I'm pleased to tell you today that I've signed legislation that will outlaw Russia forever. We begin bombing in five minutes."

The tongue-in-cheek remarks were not broadcast live, but a recording was later leaked to the public.

As a result, Soviet forces were temporarily put on high alert in the Far East, and the comments drew condemnation from the USSR.

2. Jacques Chirac doesn't like British or Finnish food (2005)

Image caption Mr Chirac accused Britain of having the "worst food", second only to Finland

French President Jacques Chirac caused a stir with culinary comments he allegedly made during a trip to Russia.

According to French newspaper Libération, the veteran politician was speaking to his Russian and German counterparts during an event marking the 750th anniversary of Kaliningrad - Russia's enclave in northern Europe.

Thinking he was off-microphone, Mr Chirac allegedly said of the UK: "You can't trust people who cook as badly as that. After Finland, it's the country with the worst food."

"The only thing the British have ever done for European agriculture is mad cow disease," he added.

While they didn't make it to broadcast, the comments were never denied by Mr Chirac's media team.

It came at a time of cool relations between Britain and France, as the two countries clashed over farming subsidies and France's decision to abstain from involvement in the Iraq War.

3. 'Yo Blair!' (2006)

Image copyright Press Association Image caption George W Bush's unguarded comments to Tony Blair were mocked by political opponents

During a G8 Summit in St Petersburg, a private conversation - later known as "Yo, Blair" - was picked up by a microphone close to US President George W Bush and British Prime Minister Tony Blair.

During the exchange, Mr Bush appeared to greet his UK counterpart, saying "Yo, Blair, how are you doing?" He went on to thank him for the gift of a sweater, and made derogatory remarks about Hezbollah in Lebanon.

Referring to Syria's support of Hezbollah in its conflict with Israel, Mr Bush said he he hoped the UN would "get Syria to get Hezbollah to stop doing this..." followed by an expletive.

"Get Kofi [Annan] on the phone with [Bashar] Assad and make something happen," he added.

Mr Bush's use of the phrase "Yo Blair" was mocked by political opponents of both leaders. But its veracity has been questioned, with some journalists suggesting that he said "Yeah, Blair".

The recording nonetheless highlighted the leaders' close, and often controversial, relationship at the time.

4. Gordon Brown's 'bigoted woman' (2010)

Media playback is unsupported on your device Media caption Brown: "I apologise if I've said anything that has been hurtful"

While speaking with members of the public in Rochdale, northern England, Britain's then-Prime Minister Gordon Brown was confronted by a woman who queried levels of immigration.

After their exchange, Mr Brown entered his car with a Sky News microphone still pinned to his clothing.

Not realising the microphone was still on, he told an aide that the conversation "was a disaster - they should never have put me with that woman".

Asked what she had said, he replied: "Ugh, everything! She's just a sort of bigoted woman that said she used to be Labour. I mean it's just ridiculous."

Mr Brown later visited the woman - Gillian Duffy - to apologise, and repeated his apology during an interview on BBC Radio 2.

5. 'I can't stand him any more'

Media playback is unsupported on your device Media caption Journalist Dan Israel, who broke the story: ''They weren't supposed to hear it, there was a mistake''

A chat between French President Nicolas Sarkozy and US President Barack Obama was overheard by journalists at a G20 meeting in France.

Shortly before a press conference, reporters were handed translation boxes but were told not to plug their headphones in until the leaders' backroom conversation had finished.

Several people ignored the instructions and heard Mr Sarkozy talking to Mr Obama about Israeli Prime Minister Benjamin Netanyahu.

"I can't stand him any more, he's a liar," Mr Sarkozy said.

"You may be sick of him, but me, I have to deal with him every day," replied Mr Obama.

For several days there was media silence in France about the exchange, but Dan Israel of the French news website Arret sur Images later broke the story.

The exchange highlighted Israel's strained relationship with both France and the US at the time.

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