Ahmet Ozel, a lawyer for Erdogan, made an application to an Istanbul civil court for 1.5 million Turkish liras ($380,000, 320,000 euros) in compensation for "spiritual damage" from Republican People's Party (CHP) leader Kemal Kilicdaroglu, state-run news agency Anadolu reported.
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Kilicdaroglu on Tuesday demanded to know whether Erdogan was "aware" that his family, including his children, were "sending millions of dollars of money to tax havens", the Anadolu news agency reported.
"Do your children have millions of dollars sent to overseas accounts?" Kilicdaroglu asked during the CHP group meeting in parliament.
The comments were "slander" against the president, Ozel said, describing them as "humiliating, insulting, false accusations", Anadolu reported.
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The move comes after Turkish prosecutors launched an investigation last month into CHP spokesperson Bulent Tezcan on charges of "insulting the president" after he called Erdogan a "fascist dictator".
A similar investigation was launched in 2016 against Kilicdaroglu after he repeatedly called Erdogan a "tinpot dictator".
Thousands of Turks have been prosecuted in recent years for allegedly insulting Erdogan but most of the complaints did not lead to jail time.
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