Turkish President Tayyip Erdogan said on Saturday he had ordered the foreign ministry to declare 10 ambassadors from Western countries 'persona non grata' for calling for the release of philanthropist Osman Kavala.

Kavala has been in prison for four years, charged with financing nationwide protests in 2013 and with involvement in a failed coup in 2016. He denies the charges.

In a joint statement on Oct. 18, the ambassadors of Canada, Denmark, France, Germany, the Netherlands, Norway, Sweden, Finland, New Zealand and the United States called for a just and speedy resolution to Kavala's case, and for his "urgent release". They were summoned by the foreign ministry, which called the statement irresponsible.

"I gave the necessary order to our foreign minister and said what must be done: These 10 ambassadors must be declared persona non grata at once. You will sort it out immediately," Erdogan said in a speech in the city of Eskisehir in northwest Turkey.

"They will know and understand Turkey. The day they do not know and understand Turkey, they will leave," he said to cheers from the crowd.

The U.S., German and French embassies and the White House and U.S. State Department did not immediately respond to requests for comment.

Kavala was acquitted last year of charges related to the 2013 protests, but the ruling was overturned this year and combined with charges in another case related to the coup attempt.

Rights groups say his case is emblematic of a crackdown on dissent under Erdogan.

Kavala said on Friday that it would be "meaningless" for him to attend his trial as a fair hearing was impossible given recent comments by Erdogan.

Erdogan was cited on Thursday as saying the ambassadors in question would not release "bandits, murderers and terrorists" in their own countries.

"Since there is no possibility of a fair trial under these circumstances, I believe participating in hearings and delivering my defence will be meaningless from now on," Kavala said in a written statement.

The European Court of Human Rights called for Kavala's immediate release in late 2019, saying there was no reasonable suspicion that he had committed an offence, and finding that his detention had been intended to silence him. 

It issued a similar ruling this year in the case of Selahattin Demirtas, former head of the pro-Kurdish Peoples' Democratic Party (HDP), who has been held in jail for nearly five years.

The Council of Europe, which oversees the implementation of ECHR decisions, has said it will begin infringement proceedings against Turkey if Kavala is not released.

The next hearing in the case against Kavala and others is due on Nov. 26.