Cartoonist Luz, who drew Charlie Hebdo's front cover picture of Muhammad following the massacre of the satirical weekly's editorial team in January, said Monday he was leaving the paper.

Renald Luzier said his departure in September was unconnected to internal tensions at the publication, but rather that the job without his slain colleagues had become "too much to bear."

"This is a very personal choice," Luz, who joined Charlie Hebdo in 1992, said in an interview with French newspaper Liberation.

"Each issue is torture because the others are gone. Spending sleepless nights summoning the dead, wondering what Charb, Cabu, Honore, Tignous would have done is exhausting," the cartoonist said, referring to his colleagues killed in the attack on January 7.

The provocative weekly became a household name after two Islamist brothers gunned down 12 people at the publication's offices over its cartoons lampooning the Prophet Muhammad.

Luz penned the magazine's first cover image a week after attacks, which portrayed Muhammad with a sign saying "Je Suis Charlie" under the words "All is forgiven."

The issue had a print run of eight million - a record for the French press.

In late April, however, Luz announced that he would not draw the prophet again, saying the drawings no longer interested him.

"Many people push me to keep going, but they forget that the worry is finding inspiration," Luz told Liberation.