Turkey’s President Recep Tayyip Erdogan addresses after he received a honorary doctorate from the Uludag University in Bursa, Turkey.

Turkish prosecutors on Monday launched an investigation into the head of Turkey’s main opposition party after he called President Recep Tayyip Erdogan a “tinpot dictator”.

Kemal Kilicdaroglu was speaking out against the detention of Turkish academics last week over a petition condemning the military crackdown in the Kurdish-dominated southeast, just days after Erdogan threatened the signatories.

“Academics who express their opinion are being detained, one by one, because of a tinpot dictator,” Kilicdaroglu told a congress of his Republican People’s Party (CHP) at the weekend.

“How dare you (Erdogan) send police to these peoples’ doors and have them detained.”

“Tell us, tinpot dictator, what do honour and pride mean to you? Either you maintain your impartiality and get respect or I will remind you every day what honour and pride mean.”

The chief prosecutor’s office in Ankara launched the probe against Kilicdaroglu on charges of “openly insulting the president,” the official Anatolia news agency reported.

The crime is punishable by up to four years in prison.

Erdogan has separately filed a civil lawsuit against Kilicdaroglu, seeking 100,000 Turkish Liras ($33,300) in compensation for “slander” from the CHP leader, the private NTV channel said.

Justice Minister Bekir Bozdag on Monday slammed Kilicdaroglu over the dictator jibe, writing on Twitter: “I pity Mr. Kilicdaroglu for not being able to criticize our dear president without insulting him.”

“Only those who lack intelligence, knowledge, and morality can insult others like that under the disguise of freedom of expression.”

Erdogan had in June last year filed a lawsuit against Kilicdaroglu for “slander” for claiming the president’s vast palace in Ankara had gold-plated toilet seats.

Concerns have mounted in recent months over freedom of expression in Turkey, in particular over the spiraling numbers of Turks being taken to court on charges of insulting Erdogan, accused by his opponents of increasing authoritarianism.

Prosecutors on Thursday began a vast investigation into over 1,200 academics for engaging in “terrorist propaganda” by signing a petition urging Ankara to halt “its deliberate massacres” in the Kurdish-majority region.

On Friday Turkish police detained at least 18 of them, sparking fresh international concern at restrictions on freedom of expression in Turkey.

Turkey is waging an all-out offensive against the separatist Kurdistan Workers’ Party (PKK), with military operations backed by curfews aimed at flushing out rebels from several southeastern urban centres.

Human rights activists say dozens of civilians have died as a result of excessive force.

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