ANKARA (Reuters) - Turkey has ordered the arrest of the Muslim cleric Fethullah Gulen and seven others over the 2016 assassination of the Russian envoy to Turkey, the Haberturk newspaper said on Monday, a day before Russian President Vladimir Putin visits the country.

U.S.-based Turkish cleric Fethullah Gulen at his home in Saylorsburg, Pennsylvania, U.S. July 10, 2017. REUTERS/Charles Mostoller

Andrei Karlov was shot dead by an off-duty policeman while speaking at an Ankara exhibit opening in December 2016. The gunman shouted “Allahu Akbar” and “Don’t forget Aleppo!” as he opened fire, apparently referring to Russia’s involvement in neighboring Syria. He was shot dead by police at the scene.

Putin arrives on a two-day visit on Tuesday and will meet President Tayyip Erdogan and Iranian President Hassan Rouhani. Their three countries are the guarantors of the Astana peace talks that has set up “de-escalation” zones across war-torn Syria.

Erdogan said Gulen’s movement was behind the assassination, a charge the cleric has denied. Erdogan also blames the preacher’s network for an attempted military coup in July 2016.

Gulen, who has lived in self-imposed exile in the United States since 1999, has denied the charge and condemned the coup.

Haberturk said the authorities ordered the arrests of the eight as the killing was carried out on their orders.

Authorities have so far arrested seven others, including three policeman, in relation to the killing, the Hurriyet newspaper reported.

No one was immediately available for comment at the Ankara prosecutor’s office.

The gunman came from Soke in southwest Turkey, considered one of the country’s most secular regions. His father said his son’s behavior started changing after he joined the police academy, where he became more pious, according to media reports at the time.

While the slogans he shouted suggest he was sympathetic to radical Islamist ideology, Gulen’s network preaches interfaith dialogue. The Turkish government says such teachings are designed to mask the true nature of what they call a dangerous, secretive organization.