A spate of violence over the past several months has posed numerous challenges to social media companies. Friday's unsuccessful military coup in Turkey was marked first by restrictions on social media, internet monitoring groups said, but the crackdown appeared to ease as the events unfolded and numerous citizens broadcast live video on Facebook and sent tweets.

U.S. and French authorities on Friday were still trying to determine whether the Tunisian man who drove a truck into Bastille Day crowds on Thursday, killing 84 people, had ties to Islamic militants.

At least 50 Twitter accounts praising the attacks used the hashtag Nice in Arabic, according to the Counter Extremism Project, a private group that monitors and reports extremist content online. Many accounts appeared almost immediately after the attack and shared images praising the carnage, the group said.

The pattern was similar to what was seen on Twitter after attacks last year and earlier this year in Paris and Brussels. But Twitter, which once took a purist approach to free speech but has since revised its rules, took action much more quickly this week. Twitter has always had policies banning violent content, such as advocacy of terrorism, and recently made them more explicit.

"Twitter moved with swiftness we have not seen before to erase pro-attack tweets within minutes," Counter Extremism Project said in a statement. "It was the first time Twitter has reacted so efficiently."

Rabbi Abraham Cooper, head of the Simon Wiesenthal Center's Digital Terrorism and Hate project, also said Twitter had responded with unusual alacrity.

Twitter did not provide any information about account suspensions, but said in a statement that it condemns terrorism and bans it on its site.

Twitter, Facebook Inc and other internet firms have ramped up their efforts over the past two years to quickly remove violent propaganda that violates their terms of service.

Both companies continue to face major challenges in distinguishing between graphic images that are shared to glorify or celebrate attacks and those shared by witnesses who are documenting events.

REUTERS