Canada's foreign minister has resigned in a scandal over misplaced top-secret files and a former model with links to the Hell's Angels.

Maxime Bernier quit after admitting leaving the classified documents at the home of exgirlfriend Julie Couillard.

Canadian prime minister Stephen Harper called the lapse a 'serious error'.

Controversy: Maxime Bernier with Julie Couillard in Ottawa, Ontario

The nature of the file remains unknown. But Canadian media sources speculated that it included classified information from last year's NATO summit in Romania.

One sensitive document was said to include details of NATO's military strength in Afghanistan.

Mr Bernier, 45, has earned the nickname Mad Max for a series of gaffes including promising aid for Burma on a plane that wasn't available.

His relationship with Miss Couillard, 39, who was married to one Hell's Angel biker and lived with another, has caused particular controversy.

But he appeared to have weathered all the storms  -  until the couple went through an ugly break-up.

Controversy: Prime Minister Stephen Harper

Mr Bernier was told on Sunday that his ex-girlfriend would appear on TV the next day to accuse him of being 'careless' with government documents.

So he got in first. In a letter to Mr Harper on Sunday, he wrote: 'The security breach that occurred was my fault and my fault alone and I take full responsibility for my actions.'

Mr Bernier's relationship with Miss Couillard first hit the headlines last August when she appeared alongside him at his swearing-in ceremony wearing an extremely low-cut sundress.

Their romance came under even greater scrutiny when it emerged she had lived with Hell's Angel Gilles Giguere, who died in a gangland-style attack in 1996, and was once married to Stephane Sirois, who was close to the leader of the notoriously violent group.

Miss Couillard made no attempt to deny her past ties, acknowledging that the two men were 'not choir boys'.

But she insisted: 'I am definitely not a biker's chick.'

In her emotional interview on Monday, she accused the foreign minister of a 'serious lack of judgment'.

She said that he had encouraged her to wear the revealing dress in August because of the press coverage he would gain.

Even more damaging were her remarks about the classified file. 'Maxime came to see me and he left a document behind,' she said, adding that she had handed it back to officials.

Miss Couillard said she decided to go public with her side of the story because of the intense media coverage in recent days.

'He is the politician and he should have warned me that the world of politics can be played below the belt,' she added.

Miss Couillard was said to have been particularly angered by recent government claims that Mr Bernier did not know about her previous relationships until they were revealed in the Canadian press.

She says he was fully aware of her 'rough' past and was compassionate about it.

As his girlfriend, she dined with Canada's prime minister and met President Bush. Recounting the meeting last year, she said the president told Mr Bernier after meeting her: 'Well, well, well, haven't you been keeping good company.'

She said she tried to end the relationship in December but the couple continued seeing one another occasionally.

She said Mr Bernier had told her: 'I can't switch girlfriends like I change shirts, so you have to be my official girlfriend for at least a year, in spite of what might happen between us.'