PARIS — The Paris prosecutor’s office has opened an investigation into death threats against the French satirical newspaper Charlie Hebdo, which was the target of a sophisticated terror attack in 2015.

Office spokeswoman Agnes Thibault-Lecuivre said Wednesday that the investigation for “written death threats” follows about a dozen postings in July and August on the paper’s Facebook page, which carried a cover cartoon mocking Muslims at the beach.

The investigation came after the newspaper filed a police complaint on Thursday, a shareholder said.

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Eric Portheault told AFP the threats began in mid-July but mounted on Tuesday after the magazine released its latest edition. The threats “do not stop,” Portheault said.

Charlie Hebdo posted its latest cover on its Facebook page on Tuesday, of a bearded man and a veiled woman running naked on the beach, with the message “Musulmans… Dé-coin-cez-vous !” which loosely translates to “Muslims, free yourselves!”

“We cannot let threats, insults, racist statements come to pass. It’s unacceptable. Especially death threats. On August 10, we were told [there would be]’an attack in 20 days,'” Portheault said.

The threats began in July after the release of a drawing for the Euro 2016 championships depicting French footballer Antoine Griezmann as a vibrator with a message that translates to “stimulate us.”

In June, a separate complaint was opened for other written threats against the newspaper.

An attack on the Charlie Hebdo newsroom killed 12 people on January 7, 2015. Two brothers claiming to be members if al-Qaeda in the Arabian Peninsula claimed responsibility, saying it was in retaliation for the newspaper’s depictions of the Prophet Muhammad.

The attack was part of a three-day assault waged by brothers Cherif and Said Kouachi and their accomplice Amedy Coulibaly who killed four Jewish men at a kosher supermarket in Paris after taking dozens hostage. That attack, which Coulibaly claimed he carried out in the name of the Islamic State terror group, occurred two days after the magazine massacre and a day after Coulibaly shot dead a policewoman, also in the capital.