Canadian Prime Minister Justin Trudeau defended free speech on Friday, but added that it was "not without limits" and should not "arbitrarily and needlessly hurt" certain communities. 

"We will always defend freedom of expression," Trudeau said in response to a question about the right to show cartoons deeply sensitive to Muslims, as France's Charlie Hebdo magazine did.

"But freedom of expression is not without limits," he added. "We owe it to ourselves to act with respect for others and to seek not to arbitrarily or unnecessarily injure those with whom we are sharing a society and a planet."

"We do not have the right for example to shout fire in a movie theatre crowded with people, there are always limits," he argued.

His comments came days after a man killed 3 people in a Church in France. The attack came after French President Emmanuel Macron's controversial decision to show the cartoons across the country after a teacher was killed for showing those in classroom.

Distancing himself from the position of French Macron, Trudeau pleaded for a careful use of free speech.

"In a pluralist, diverse and respectful society like ours, we owe it to ourselves to be aware of the impact of our words, of our actions on others, particularly these communities and populations who still experience a great deal of discrimination," he said.

Meanwhile, the French government has vowed to send thousands more police onto the streets to ensure security as investigators sought to uncover what motivated a young Tunisian to kill three people inside a church in the southern city of Nice.

The bloodshed inside Nice's Notre-Dame basilica on Thursday morning added new tension in a country already on the highest alert after a string of attacks blamed on suspected Islamists in recent weeks.

The 21-year-old Tunisian arrived in France this month via Italy before carrying out what the government described as an act of "Islamist" terror inside the church.

The suspected knifeman, identified as Brahim Issaou, was shot multiple times by police in the aftermath of the attack. He has been in serious condition and was not conscious as of Friday evening, a source close to matter told AFP.

A source close to the investigation, who asked not to be named, said the authorities believe Issaou arrived in Nice no more than 48 hours before the attack.