Turkish President Recep Tayyip Erdogan says the Turkish policeman who gunned down the Russian ambassador in Ankara was a member of the network of Muslim cleric Fethullah Gulen.
"There is no reason to hide that he's a member of the FETO network. All his connections, from where he was educated to his links, point to FETO," Erdogan said at a news conference on December 21.
Turkish authorities refer to the followers of the U.S.-based Gulen as the "Gulenist Terrorist Network" (FETO).
Gulen himself has condemned the assassination of ambassador Andrei Karlov, calling it a "heinous act of terror."
The envoy was shot nine times while speaking at an art exhibition on December 19. The off-duty policeman, who authorities identified as Mevlut Mert Altintas, was later killed by police.
Altintas shouted "Don't forget Aleppo" and various Islamic slogans at the scene of the murder before he was killed.
On December 20, the Turkish Foreign Ministry quoted Foreign Minister Mevlut Cavusoglu as telling U.S. Secretary of State John Kerry in a phone conversation that "Turkey and Russia know that behind the attack...there is FETO."
However, Russian President Vladimir Putin's spokesman said on December 21 that one should not "rush to conclusions before the investigation determines who was behind the killing."
"Moscow believes that it's necessary to wait for the results of the joint investigative group's activity," Kremlin spokesman Dmitry Peskov said, referring to an investigation by Turkish and Russian authorities.
Turkey has demanded the extradition of Gulen, who lives in exile in the U.S. state of Pennsylvania, in connection with a failed coup attempt against Turkish President Recep Tayyip Erdogan in July. Ankara has chafed as the U.S. Justice Department has so far refused to extradite Gulen, saying that Turkey must present compelling evidence implicating him.
Some Turkish officials in recent days have suggested that the United States supported the assassination of Karlov, prompting a sharp rebuke from U.S. State Department spokesman John Kirby on December 20.
Kirby said Kerry raised concerns about "some of the rhetoric coming out of Turkey with respect to American involvement or support, tacit or otherwise, for this unspeakable assassination yesterday because of the presence of Mr. Gulen here in the United States."
"It's a ludicrous claim, absolutely false. There's no basis of truth in it whatsoever," Kirby said. "And the secretary made that very clear in his discussions today with the foreign minister.
"We need to let the investigators do their job and we need to let the facts and the evidence take them where it is before we jump to conclusions," Kirby said.
Kerry reportedly offered U.S. assistance to Turkey in investigating the killing. However, Ankara has said it will jointly investigate with Russian authorities, and Moscow dispatched a team of about 20 investigators to Turkey on December 20.
Gulen, a reclusive figure who preaches interfaith dialogue and whose followers and organizations are best known for sponsoring schools and charitable causes, has condemned what he called the "heinous act of terror" that killed Karlov.
While Turkish authorities are seeking to determine whether Altintas had ties to Gulen, the slogans he shouted may be more closely associated with a radical Islamist group in Syria that has ties to Al-Qaeda.
One slogan in particular shouted by Altintas -- "We are the ones who swore allegiance to [the Prophet] Muhammad for the jihad!" -- was commonly used in propaganda videos of Syria's Jabhat al-Nusra militant group, according to Turkey's Hurriyet newspaper.
Jabhat al-Nusra, which changed its name to Fatah al-Sham, is one of the rebel militias that Syrian regime forces are now pushing out of Aleppo as they clinch their grip on the city.