Canadian Foreign Minister Maxime Bernier resigned on Monday after it emerged he had left classified documents in the apartment of a former girlfriend who was once linked to organised crime figures.

"Minister Bernier has learned, and informed me, that he left classified government documents in a non-secure location. This is a serious error. (He) has accepted his responsibilities in offering to resign," said Prime Minister Stephen Harper.

Bernier, 45, had been under increasing pressure to quit amid revelations about the personal life of Julie Couillard, the former girlfriend. Couillard said Bernier had forgotten a document in her apartment in April.

"He came to my place, then he left, and the document remained with me," she told the French-language TVA network in an interview shown late on Monday. She said she had given the document to a lawyer who returned it to the government.

Trade Minister David Emerson will replace him on a temporary basis.

Bernier, who took over the job last August, had also been under fire for a series of recent gaffes.

Most notably, he embarrassed Ottawa in April by openly suggesting that Afghan President Hamid Karzai replace the governor of Kandahar province. Canada has 2,500 troops based in the southern Afghan city.

Bernier was the first minister to quit the cabinet under a cloud since the Conservatives won power in January 2006 on a promise to clean up federal politics.

A grim-faced Harper, speaking just hours before departing on a trip to Europe, insisted Bernier's departure had nothing to do with his relationship with Couillard.

"This is about one thing and that is a failure to uphold expected standards on government documents. It is a very serious mistake, regardless of who the minister is, regardless of personal life," he said.

Couillard had once been involved with a member of a biker gang who was assassinated. She later married a biker gang member but they quickly divorced.

She conceded that neither man had been an innocent but added: "I have done nothing to embarrass my country."

Bernier's resignation spectacularly ends the political career of a man who some believed could eventually challenge for the position of prime minister. It also removes a foreign minister who looked out of his depth from the start.

Bernier had been industry minister when Harper asked him to take over at foreign affairs and sell the Afghan mission to the politically influential French-speaking province of Quebec, where anti-war sentiment is traditionally high.

The new minister made one speech in Quebec on the mission but then disappeared from view over the file, only regaining the spotlight when details of his ties to Couillard came to light.

All three opposition parties blasted Harper for not providing more details about the documents.

"Obviously Mr. Bernier has been suffering from an accumulation of blunders over the past number of weeks. The issue has now come to a breaking point," senior Liberal legislator Ralph Goodale told reporters.

"The prime minister has a lot of explaining to do."

Couillard, who first came to public attention last August when she was pictured in a very revealing dress alongside Bernier, also said President George W. Bush had paid her a compliment at a reception at the United Nations last year.

"Well well well, haven't you been keeping good company," she quoted Bush as telling Bernier.