Prime Minister Ahmet Davutoğlu accused the head of Turkey’s pro-Kurdish opposition party of treason on Thursday for using a trip to Moscow to condemn Ankara’s shooting down of a Russian warplane over Syria.

Selahattin Demirtaş, co-head of the Peoples’ Democratic Party (HDP), met foreign minister Sergei Lavrov in Moscow on Wednesday and criticized Ankara for shooting down the warplane near the border with Syria last month. Moscow denies it had entered Turkish airspace.

“They take sides with whoever Turkey is facing a crisis with. Demirtaş saying in Moscow that Turkey’s downing of Russian jet was wrong is a total disgrace and treason,” Davutoglu told a meeting of businessmen in Ankara.

“Our main duty is to raise our voice against Russian cruelty. Supporting Russia while it kills civilians in Syria is treason not only against this country, but also against humanity.”

Lavrov told Demirtaş Russia was ready to cooperate closely with ethnic Kurds fighting against Islamic State militants in Iraq and Syria.