As the investigation into the murder of Ambassador Andrey Karlov continues in Ankara, a high level source said that based on current evidence, the Russian side is convinced that the Gülenist Terror Group (FETÖ) was behind the assassination and Russia may consider requesting the extradition of FETÖ leader, Fetullah Gülen, after the completion of the investigation."The Russians are convinced that FETÖ was behind the assassination of Ambassador Andrey Karlov. The Russian side is also likely to start the process of extraditing of Gülen from the U.S," a high level source in the Turkish Presidency said. "This means a global war against FETÖ and the U.S cannot ignore both Turkey and Russia's extradition request," a high level source added.

On Dec. 20, Foreign Minister Mevlüt Çavuşoğlu told his U.S. counterpart John Kerry that both Russia and Turkey are aware of Gülen's involvement in the assassination of the Russian envoy. In addition, President Recep Tayyip Erdoğan said on Dec. 21 that the slain Russian ambassador Andrey Karlov's assassin was "obviously" a member of FETÖ in a press conference with his Albanian counterpart. "The assassin of the Russian ambassador is obviously a member of FETÖ. There is no need to hide it," the president said. "Where he grew up, and all the connections reveal this [FETÖ membership]," he added.FETÖ is run by fugitive imam Fetullah Gülen who lives in self-imposed exile in the foothills of the Pocono Mountains in rural Pennsylvania. Through his middlemen and militants embedded in the key institutions of the state and the military, the top terrorist tried to overthrow Turkey's democratically elected governments in the Dec. 17-25 operations and the July 15 military coup bid, both of which failed.