TBILISI - A former Islamic State warlord suspected of masterminding a deadly attack on Istanbul airport in 2016 is believed to have been killed during a special operation in ex-Soviet Georgia last week, three sources familiar with the case told Reuters.Akhmed Chatayev, an ethnic Chechen, is highly likely to have been killed during a police operation against a group of armed men on the outskirts of the Georgian capital Tbilisi last week, the three sources said.One Georgian special forces serviceman and three members of the armed group, which was suspected of terrorism, were killed in the operation. Four police officers were wounded and one member of the group was arrested during the 20-hour operation at the apartment block where the group was hiding."We suspect that one of the gunmen killed in the special operation in Tbilisi could be Akhmed Chatayev," Nino Giorgobiani, deputy chief of the state security service, told Reuters on Tuesday.She said that the final conclusions would be reached after experts had completed their work and "the relevant United States agencies (had) joined the investigation."Two other sources, who did not want to be named, told Reuters it looked very likely Chatayev had been killed."There is every indication that one of them (members of the group) was Chatayev," said one of the sources."According to my information, Chatayev was there... He blew himself up," said the other source.Chatayev was named by Turkish media and a US congressman as the mastermind of the suicide bombing of Istanbul airport in 2016 which killed 45 people. His involvement in the airport bombing has not been confirmed by Turkish officials.A veteran of Chechnya's conflict with Moscow during which he lost an arm, he lived in Georgia's Pankisi Gorge, a remote area populated largely by people from the Kist community, ethnic Chechens whose ancestors came to mainly Christian Georgia in the 1800s.When, after the collapse of the Soviet Union, Chechnya rose up in an armed rebellion against Moscow's rule, the Kist community were drawn to the fight. Thousands of refugees arrived from Chechnya, and some insurgents used the gorge to regroup and prepare new attacks.Chatayev was wounded and arrested in Georgia in August 2012 following a clash between the Georgian police and a group of militants, who were allegedly trying to cross the Georgian-Russian border and move to Dagestan.He was released from jail on bail and Georgian prosecutors dropped the case against him in January 2013, citing a lack of evidence. Soon after his release, Chatayev left Georgia, saying he intended to go to Austria to convalesce. By 2015, he had moved to Islamic State-controlled areas in Syria and Iraq.Chatayev was listed as a terrorist in 2015 by the US Treasury which accused him of planning attacks against unspecified US and Turkish facilities and added him to the UN Security Council's Al-Qaeda sanctions list.He was also wanted by the Russian authorities.