Pope Francis says there are limits to freedom of speech, especially when it comes to someone's religion, in comments aboard the Papal Plane that made reference to the deadly attack last week on the French satirical magazine Charlie Hebdo.

Francis defended freedom of speech, calling it a fundamental human right, but said it must not cause offense.

"It is true we cannot react violently," he told reporters today en route to the Philippines. "But if Dr. [Alberto] Gasbarri here, a great friend, were to say something insulting against my mother, a punch awaits him."

Gasbarri, the official who organizes papal trips, was standing next to the pope at the time of the comments.

"You cannot make provocations," Francis added. "You cannot insult people's faith."

But the pope reiterated his previous comments about the attack on Charlie Hebdo, calling it an "aberration."

"Killing in the name of God is an aberration against God," he said. "I think this is the main thing with freedom of religion. You can practice with freedom but without imposing or killing."

You can watch an excerpt of the comments here.

Charlie Hebdo has a long history of lampooning religion, and its portrayals of Islam's Prophet Muhammad resulted in the attacks that killed some of its most famous cartoonists.

Some Muslims consider any depiction of their prophet – even positive ones – offensive.

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