A Chechen extremist was the mastermind behind the triple suicide bombing at Istanbul's busiest airport which killed at least 44 people, a US congressman has said.
Michael McCaul, chairman of the House Committee on Homeland Security, told CNN that Akhmed Chatayev directed Tuesday night's gun-and-bomb attack at Ataturk Airport, which also wounded more than 230 other people.
Turkish and Swedish media have also identified Chatayev as the organiser, although Turkish authorities have not confirmed his involvement.
Swedish authorities said Chatayev was convicted of weapons smuggling in 2008.
The city court in the southern Swedish port city of Ystad said he was sentenced to 16 months for smuggling an automatic weapon and two handguns with munition and silencers into Sweden on March 3 2008.
Court documents show Chatayev had arrived by ferry boat from Germany. He and two others in the car said they were heading to Norway to go fishing and meet friends.
The documents show he denied knowing about the guns hidden in a spare wheel in the trunk. A local paper said he was freed from prison in January 2009.
Mr McCaul said it is unclear where Chatayev is, but he is known to have served as a top lieutenant in Islamic State's war ministry.
Turkey's Sabah newspaper, which is close to the government, said police had launched a manhunt to catch the alleged mastermind.
Although no group has claimed responsibility, the IS group is the main suspect for the airport attack. The group has boasted of having cells in Turkey, among other countries.
Authorities said the three suicide bombers in the attack - which echoed the carnage earlier this year at the Brussels airport - were from Russia and the Central Asian nations of Uzbekistan and Kyrgyzstan. They did not provide further details on their identities.
Thirteen people suspected of possible links to the attack were detained in raids in three Istanbul neighbourhoods on Thursday, officials said.
The Haber Turk newspaper said that 11 more suspects - all of them foreign nationals - were detained in a separate raid on a house in Istanbul early on Friday. A government official in Istanbul could not immediately confirm the report.