The right-wing extremist charged over the attacks in Christchurch apparently published a manifesto online that Turkish media said contained specific references to Turkey and ridding the famed Hagia Sophia in Istanbul of its minarets.
On Saturday around 500 protesters gathered outside the Hagia Sophia, which is now a museum but was once a church before being turned into a mosque during the Ottoman empire.
The crowds of mainly nationalist and Islamic groups unfurled banners that read "Muslims, stand tall!" and "Muslims, unite!" and conducted a short prayer service for the victims.
Police stepped up security around the building, with dozens of officers flanking the demonstration, some on horse back and others carrying riot shields.
"Everyone is aware of the rising Islamophobia all over the world; assailants find the courage to launch such attacks because of Muslims' timidity," said Faruk Hanedar, one of the demonstrators.
"We are here to show Muslims are able to respond to them with a smart attitude," he added.
Players observed a minute of silence for all the victims ahead of a football match Friday night between Istanbul giant Fenerbahce and Sivasspor. Football fans at Fenerbahce's stadium chanted "Allahu Akbar" (God is greatest).
The Friday attacks on worshippers are thought to be the worst act of terror against Muslims in the West and have sparked an outpouring of grief and horror across the globe.
"With this attack, hostility towards Islam, that the world has been idly watching and even encouraging for some time, has gone beyond individual harassment to reach the level of mass killing," Erdogan said.
Hundreds of people gathered in Athens on Saturday in a rally against Islamophobia, in a protest called by activists that had been planned for several weeks.
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