A Turkish policeman crying "Aleppo!" fatally shot Russian Ambassador Andrei Karlov while he was addressing visitors to a photo exhibition earlier in the day.
Ankara mayor Melih Gokcek had earlier speculated on his official Twitter account that the gunman may have been linked to the exiled preacher, whom the government blames for the July coup aimed at toppling President Recep Tayyip Erdogan.
"I condemn in the strongest terms this heinous act of terror," Gulen said in a statement yesterday.
Gulen, who has been based in the United States since the late 1990s, has vehemently denied the claims of his involvement in the coup.
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The comments by Gokcek, the Ankara mayor, were echoed today by the pro-government press, which also alleged the gunman had ties to Gulen. However, no ministerial-level official has repeated the claims so far.
"Turkish and international experts repeatedly have pointed out the deterioration of security and counter-terrorism efforts due to the Turkish government's assigning hundreds of counter-terrorism police officers to unrelated posts, as well as the firing and imprisoning (of) many others since 2014," Gulen said.
He also urged Turkey and Russia to work toward resolving the Syrian conflict.
"This despicable act of shooting an ambassador, who represents an entire nation, only exacerbates the Syrian conflict that has already taken too many lives and driven too many from their homelands, like adding fuel to a fire.