PARIS — Demonstrators in France on Sunday took part in gatherings in support of freedom of speech and in tribute to a history teacher who was beheaded near Paris after discussing caricatures of Islam’s Prophet Muhammad with his class.

Samuel Paty was beheaded Friday by an 18-year-old Moscow-born Chechen refugee who was shot dead by police.

Political leaders, associations and unions demonstrated Sunday on the Place de la Republique in Paris holding placards reading “I am Samuel,” that echoed the “I am Charlie” rallying cry after the 2015 attack on the satirical newspaper Charlie Hebdo, which published caricatures of the Prophet Muhammad.

Demonstrators also gathered in major cities including Lyon, Toulouse, Strasbourg, Nantes, Marseille, Lille and Bordeaux.

French authorities, meanwhile, say they have detained an 11th person following the killing.

Anti-terrorism prosecutor Jean-Francois Ricard said an investigation for murder with a suspected terrorist motive was opened. At least four of those detained are family members of the attacker, who had been granted 10-year residency in France as a refugee in March and was armed with a knife and an airsoft gun, which fires plastic pellets.

His half-sister joined the Islamic State group in Syria in 2014, Ricard said. He didn’t give her name, and it wasn’t clear where she is now.

The prosecutor said a text claiming responsibility and a photograph of the victim were found on the suspect’s phone. He also confirmed that a Twitter account under the name Abdoulakh A belonged to the suspect. It posted a photo of the decapitated head minutes after the attack along with the message “I have executed one of the dogs from hell who dared to put Muhammad down.”

The beheading has upset moderate French Muslims. A group of imams in the Lyon region are holding a special meeting Sunday to discuss together what the group called “the appalling assassination of our compatriot by a terrorist who in the name of an uncertain faith committed the irreparable.”

The attack has provoked global condemnation. President Donald Trump addressed the killing Saturday night from a political rally in Janesville, Wisconsin.

“On behalf of the United States, I’d like to extend my really sincere condolences to a friend of mine, President (Emmanuel) Macron of France, where they just yesterday had a vicious, vicious Islamic terrorist attack — beheading an innocent teacher near Paris,” he said. “France is having a hard time, and Macron’s a great guy.”