ANKARA (Reuters) - President Tayyip Erdogan’s spokesman threatened a prominent opposition lawmaker with legal action on Monday for calling the Turkish leader a fascist dictator.

Turkey's President Tayyip Erdogan attends a Republic Day ceremony at Anitkabir, the mausoleum of modern Turkey's founder Mustafa Kemal Ataturk, to mark the republic's anniversary in Ankara, Turkey, October 29, 2017. REUTERS/Umit Bektas

In some of the most blistering criticism of Erdogan by a high-profile politician in recent memory, Bulent Tezcan, spokesman for the main opposition People’s Republican Party, attacked what he said was a “fearful atmosphere” in Turkey.

“If you try to scare people and to create a fearful atmosphere by showing legal words as illegal ones we will not be deterred,” Tezcan said in a speech in the western city of Tekirdag, criticizing local judicial authorities.

His comments appeared to be in defense of the local mayor, a CHP member, who was questioned by authorities this month after he reportedly called Erdogan a “dictator” at a party congress.

“I don’t know if our mayor said that or not. I, here in Tekirdag, say it now: ‘Erdogan is a fascist dictator’,” Tezcan said.

Tezcan’s comments prompted a swift backlash from Erdogan’s office and lawmakers from his ruling AK Party.

“Bulent Tezcan’s hate speech is an example of disgrace for the main opposition,” Erdogan’s spokesman, Ibrahim Kalin, said on Twitter. “This is not politics, but rather enmity towards the people’s will. Legal measures will be sought in this regard.”

Insulting the president is a crime punishable by up to four years in prison in Turkey

Lawyers for Erdogan, who has dominated Turkish politics for more than a decade, have filed more than 1,800 cases against people including cartoonists, a former Miss Turkey winner and schoolchildren on accusations of insulting him.

Following a failed coup in July 2016, Erdogan said he would drop outstanding suits, in a one-off gesture.

Nonetheless, rights groups and some Western governments have voiced concern that Turkey is sliding toward authoritarianism. Some 150,000 people have been sacked or suspended from their jobs and more than 50,000 jailed pending trial on suspicion of links to the failed coup.

Erdogan says such measures are necessary to ensure stability and defend Turkey from multiple security threats.