In a pivotal case testing the limits of free speech, the European Court of Human Rights is to decide Thursday whether denying that the mass killings of Armenians by Ottoman Turkey in 1915 were a "genocide" is a crime.
The case was sparked by a Swiss court's 2007 conviction of Turkish politician Dogu Perincek after he said publicly that the "Armenian genocide is a great international lie."
The ECHR's 17-judge Grand Chamber, whose rulings are final, will announce its decision at 0945 GMT Thursday at a brief public hearing expected to be attended by representatives of both the Turkish and Armenian communities.
The presence of prominent human rights lawyer Amal Clooney -- who represented Armenia as a third party in the case at a preliminary hearing in January -- was uncertain Tuesday.
The Swiss court in 2007 ordered Perincek, chairman of the Turkish Workers' Party, to pay a fine after finding him guilty of racial discrimination for his remarks, repeated on several occasions.
Turkey has always denied that the killings beginning in 1915 were a pre-meditated attempt by the then ruling Ottomans to wipe out the Armenians.
It also says only 500,000 died, not 1.5 million as claimed by Armenia.
Before the events, some two million Armenians were living in the territory of the Ottoman Empire.
More than 20 nations have so far recognised the killings as genocide, a definition supported by numerous historians but vehemently opposed by Turkey.
After his conviction, Perincek took the case to the ECHR, arguing that his freedom of speech was infringed.
A lower chamber of the ECHR, ruling in December 2013, rejected the Swiss court's conviction, saying that Perincek's remarks fell within the boundaries of free speech.
Switzerland appealed that ruling, and the case came before the ECHR's Grand Chamber.
In January, the Swiss side argued that denying that a genocide occurred was tantamount to "accusing the Armenians of falsifying history, one of the worst forms of racial discrimination".
On the other side, Perincek's lawyers and those of the Turkish government argued that there is no "general consensus" that the 1915 killings were genocide such as there is for the Holocaust.
Perincek's lawyer Laurent Pech said his client had "neither contested nor defended the massacres, nor did he incite hatred against the Armenians", but merely denied that the Ottoman authorities of the time had a genocidal intention.
- Bearing on Holocaust denial -
Thursday's decision may have a bearing on a case currently before France's highest court testing the constitutionality of French law prohibiting Holocaust denial.
French jurist Nicolas Hervieu, an expert on the ECHR, said a key question was whether and how the European court distinguishes between the two events.
In the initial 2013 decision the court stressed that the Perincek case must be "clearly distinguished" from those concerning Holocaust denial -- given the "historical facts, sometimes very concrete, such as the existence of gas chambers".
The latter were "considered clearly established by an international jurisdiction", it said.
"The question raised by this Perincek ruling is the overall consistency of legislation against negationism in Europe," Hervieu said.
The ECHR, whose judges come from each of the 47 members of the Council of Europe, was established by the 1953 European Convention on Human Rights.