Seven of the ambassadors represent Turkey's NATO allies and the expulsions, if carried out, would open the deepest rift with the West in Erdogan's 19 years in power.

Kavala, a contributor to numerous civil society groups, has been in prison for four years, charged with financing nationwide protests in 2013 and with involvement in a failed coup in 2016. He has remained in detention while his latest trial continues, and 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 (undesirable) at once. You will sort it out immediately," Erdogan said in a speech in the northwestern city of Eskisehir.

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

Erdogan has said previously that he plans to meet U.S. President Joe Biden at a summit of the Group of 20 (G20) major economies in Rome next weekend. read more

One diplomatic source said de-escalation was possible given Turkey has now made its stance very clear, and given the potential diplomatic fallout from such a move ahead of the G20 summit and the U.N. climate summit in Glasgow starting at the end of the month.

"No instructions have been given to embassies," the source said, adding that it was possible a decision may be taken at Turkey's cabinet meeting on Monday.

Norway said its embassy had not received any notification from Turkish authorities.

"Our ambassador has not done anything that warrants an expulsion," said the ministry's chief spokesperson, Trude Maaseide, adding that Turkey was well aware of Norway's views.

"We will continue to call on Turkey to comply with democratic standards and the rule of law to which the country committed itself under the European Human Rights Convention," Maaseide said.

'AUTHORITARIAN DRIFT'

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

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

Six of the countries involved are EU members, including Germany and France. European Parliament President David Sassoli tweeted: "The expulsion of ten ambassadors is a sign of the authoritarian drift of the Turkish government. We will not be intimidated. Freedom for Osman Kavala."

Danish Foreign Minister Jeppe Kofod said his ministry had not received any official notification, but was in contact with its friends and allies.

"We will continue to guard our common values and principles, as also expressed in the joint declaration," he said in a statement.

A source at the German Foreign Ministry also said the 10 countries were consulting with one another.

Kavala said on Friday he would no longer attend his trial as a fair hearing was impossible after recent comments by Erdogan.

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

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

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 Kavala's trial is on Nov. 26.