ISTANBUL - Four recent graduates of a top Turkish university have been arrested for displaying a cartoon mocking Turkish President Tayyip Erdogan at their graduation ceremony, according to the state-run Anadolu agency.The Middle East Technical University students in the July 6 ceremony in Ankara made and carried a long banner printed with a cartoon of animals whose faces resembled Tayyip Erdogan, entitled "The World of Tayyip."Originally published by a popular satire weekly magazine, the cartoon was the subject of a defamation lawsuit by Erdogan 12 years ago, when he was Turkey's prime minister. However, an Ankara court dismissed the case, saying the cartoon was within the limits of freedom of speech.Anadolu said the four had been "arrested ... in the course of an investigation into a sign containing defamation of Erdogan."Turkey has been waging a crackdown on dissent against Erdogan since a failed coup attempt in 2016. Erdogan has led Turkey for the past 15 years and assumed even more sweeping powers on Monday as he was sworn in as the first head of the country's new, all-powerful executive presidency.Human rights groups say the Turkish government has grown increasingly intolerant of opposition voices since a failed military coup in July 2016. The authorities have detained and formally charged 77,000 people suspected of links to the failed coup, the interior minister said in March. They have also shut down about 130 media outlets.On Friday, a Turkish court jailed six journalists for alleged links to the coup attempt, charges the rights group Amnesty International said were based solely on their articles criticizing the government.Rights groups have also decried the imprisonment of Turkish artist and journalist Zehra Dogan, who was sentenced in 2017 to nearly three years in prison for painting the wreckage of a city in southeastern Turkey where Turkish forces clashed with the Kurdistan Workers' Party (PKK) in 2016.