The Council of Europe has launched unprecedented proceedings against Turkey for failing to release philanthropist Osman Kavala.
The European human rights body has repeatedly condemned Ankara for violating's Kavala's rights by holding him in detention.
A majority of the Council's committee agreed on Wednesday that Ankara had not complied with a legally binding 2019 ruling by the European Court of Human Rights (ECHR).
It is only the second time the Council of Europe has taken disciplinary action against one of its 47 member countries. The case will now be referred back to the ECHR.
Turkey — a founding member of more than 70 years — could eventually see its voting rights suspended or face expulsion from the Council of Europe.
The European Union – which is unrelated to the Council of Europe – said the decision shows “serious concerns” about Kavala’s case.
"The initiation of infringement proceedings is a tool rarely used by the Council of Ministers of the Council of Europe,” a foreign policy spokesperson said in a statement.
Turkey's refusal to release Kavala "sets a worrying precedent and further increases the EU's concerns about the Turkish judiciary's adherence to international and European standards", they added.
Amnesty International’s Europe Director Nils Muiznieks also hailed the Council of Europe move as a “landmark decision”.
But Turkey has slammed the pan-European rights authority, accusing it of interfering with Turkey's "judicial independence".
“Whatever the Human Rights Court, whatever the Council of Europe says, it does not interest us. We expect respect to be shown to our courts," President Erdogan told a press conference in Ankara.
Kavala, 62, has been jailed in Turkey for more than four years without ever being convicted of a crime.
The businessman has been charged with financing 2013 anti-government protests and also playing a role in an attempted coup in 2016. Kavala strongly rejects the accusations.
Erdogan has repeatedly targeted the political activist and his case is still being heard by an Istanbul court.
In 2017, the Council of Europe launched infringement proceedings against Azerbaijan over its refusal to release dissident Ilgar Mammadov.