A child-pornography investigation that began in Toronto is behind a major political scandal in Germany, forcing the resignation of two prominent federal politicians, including a senior cabinet minister of Chancellor Angela Merkel's coalition government.

Agriculture Minister Hans-Peter Friedrich resigned Friday after allegations that while he was interior minister last fall he tipped off other politicians about an investigation into whether a fellow member of the German parliament had purchased nude children's images from a Toronto company.

The Canadian firm, known as Azov Films, was shut down by Toronto police during Operation Spade, a massive child-pornography probe with international ramifications that investigators only made public last November.

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According to German media, a month before Toronto police announced its operation, Mr. Friedrich informed Sigmar Gabriel, the chairman of the Social Democrat Party, that one of the SPD rising stars, Sebastian Edathy, had been targeted by Operation Spade.

At the time, after the German federal election of September, the Social Democrats were in talks to become part of Ms. Merkel's coalition government and Mr. Friedrich wanted to make sure that Mr. Edathy wouldn't be considered for a post.

Toronto police, which closed Azov and arrested its owner in 2011, seized the firm's shipping labels and customer order histories and had informed police in dozens of other countries.

Prosecutors investigating Mr. Edathy have now complained that the leak may have compromised their case, saying that the 44-year-old SDP member appeared to have received prior warning before his house and offices were raided.

"We were quite stunned to find out that apparently a broad spectrum of law-enforcement authorities had already been dealing with the Edathy case and issuing evaluations before the justice system ever gained possession of the files in question," Hanover prosecutor Joerg Froehlich told a press conference, according to German broadcaster Deutsche Welle.

As a result, German media have reported, relevant information on Mr. Edathy's computers may have been destroyed.

It is still unclear who tipped off Mr. Edathy. If it emerged that he was alerted by a senior SPD member, it could cause even greater upheaval in Ms. Merkel's coalition.

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Mr. Gabriel has denied that he and two other members of the upper echelon of his party, including Frank-Walter Steinmeier, the coalition's Foreign Affairs Minister, leaked information to Mr. Edathy about the impending probe.

Mr. Edathy resigned last week from parliament, citing health reasons.

In a statement on his Facebook account, he denied possessing or buying child pornography.

Azov Films sold mail-order DVDs and streamed online videos of naked boys from Germany, Romania and Ukraine, which it marketed as naturist movies and claimed were legal.

Prosecutors in Canada and the U.S. have deemed those images to be illicit. ‪In Canada, the Criminal Code's definition of child pornography includes images where the genitals of someone under18 are depicted for a sexual purpose.

In Germany, such material fell in a grey zone because they didn't depict explicit sexual acts but it was enough, however, to merit executing a search warrant, the prosecutor, Mr. Froehlich, said at the news conference.

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Operation Spade was a three-year investigation that led to 348 arrests around the world, from Australia to Sweden to Mexico. More than 100 suspects were charged in Canada.

The head of the company, 42-year-old Toronto resident Brian Way, has been in custody since his May, 2011, arrest. ‪A German videographer, Markus Rudolph Roth, was named as a co-conspirator.

With files from Reuters