ISTANBUL (Reuters) - Prime Minister Ahmet Davutoglu 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 Demirtas, 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. Demirtas 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."

Kurdish politicians have accused Ankara of focusing military efforts on Kurdish militia in Iraq and Syria and failing to take up the fight with Islamic State.

Russia, which imposed economic sanctions on Turkey after the Nov. 24 incident, has sharply criticized President Tayyip Erdogan. It would be keenly aware of the sensitivity of Ankara to any contacts between Moscow and Kurdish politicians.

Erdogan has accused the HDP, the second-largest opposition party in Turkey's parliament, of connections with armed Kurdish rebels fighting in Turkey's southeast.

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

(This version of the story corrects day in first paragraph to Thursday, not Friday)

(Reporting by Tulay Karadeniz and Ece Toksabay; Writing by David Dolan; Editing by Ralph Boulton)