Twitter confirmed that several of its accounts were hacked on Wednesday morning, after they tweeted Turkish messages with Swastika symbols. Messages reading “#NaziGermany👌#NaziNetherlands, a little👋#OTTOMAN SLAP for you, see you on #April16th,” were tweeted from thousands of accounts, including those of BBC North America, Forbes, Amnesty International, tennis star Boris Becker.

“Our teams are working at pace and taking direct action on this,” Twitter said in a statement according to The Guardian. The social media platform added that the source of the attack had been tracked to a third party application, Twitter Counter. The application is used to monitor Twitter statistics.

April 16 is when Turkey is planning to hold a referendum to decide whether or not to grant stronger powers to its President Tayyip Erdogan. Last week, Turkish leaders were banned by Netherlands and several German towns from holding rallies for the referendum, AFP reported. Erdogan had accused Germany of “Nazi” practices.