The three suicide bombers who carried out a deadly attack on Istanbul's main airport were of Russian, Uzbek and Kyrgyz nationality, a Turkish official said on Thursday.
Police detained 13 people, three of them foreigners, in raids across Istanbul in connection with Tuesday's attack on Europe's third-busiest airport, the deadliest in a series of suicide bombings in Turkey this year.
Counter-terrorism teams led by police special forces launched simultaneous raids at 16 locations in the city, two officials told Reuters. Turkish authorities have said they believe the extremist group Islamic State in Iraq and Syria was behind the airport attack.
Meanwhile, the death toll from the attack climbed to 44 on Thursday, according to Turkey's interior minister.
The pro-government Yeni Safak newspaper earlier said the bombers were from Kyrgyzstan, Uzbekistan and Dagestan in southern Russia, without naming its sources. Dagestan borders Chechnya, where Moscow has led two wars against separatists and religious militants since the Soviet Union collapsed in 1991.
The Kyrgyz security service declined to comment, while the Uzbek security service could not immediately be reached.
Around the clock
Three bombers opened fire to create panic outside the airport in Tuesday's attack, before two of them got inside and blew themselves up. The third detonated his explosives at the entrance. A further 238 people were wounded.
Yeni Safak said the organizer of the attack was suspected to be a man called Akhmed Chatayev, of Chechen origin. Chatayev is identified on a United Nations sanctions list as a leader in ISIS responsible for training Russian-speaking militants, and as wanted by Russian authorities.
The Hurriyet newspaper named one of the attackers as Osman Vadinov, also Chechen, and said he had come from Raqqa, the heart of ISIS-controlled territory in Syria.
Turkish officials did not confirm to Reuters that either Chatayev or Vadinov were part of the investigation.
Wars in neighbouring Syria and Iraq have fostered a home-grown ISIS network blamed for a series of suicide bombings in Turkey, including two this year targeting foreign tourists in the heart of Istanbul.
ISIS has established a self-declared caliphate on swathes of both Syria and Iraq and declared war on all non-Muslims plus Muslims who do not accept its ultra-hardline vision of Sunni Islam. It has claimed responsibility for similar bomb and gun attacks in Belgium and France in the past year.
Turkey, a member of the NATO military alliance and part of the U.S.-led coalition against ISIS, has repeatedly fired back on the Sunni hardliners in recent months after rocket fire from northern Syria hit the border town of Kilis.
In a sign of the growing threats to Turkey, U.S. defence sources said on Wednesday that Washington was moving towards permanently banning families from accompanying U.S. military and civilian personnel deployed in the country.
Critics say Turkey woke up too late to the threat from ISIS, focusing instead in the early part of the Syrian civil war on trying to oust President Bashar al-Assad, arguing there could be no peace without his departure.
Once a reluctant partner in the fight against ISIS, Ankara adjusted its military rules of engagement this month to allow NATO allies to carry out more patrol flights along its border with Syria.
It has also carried out repeated raids on suspected ISIS safe houses in Turkey.
Nine suspected militants, thought to have been in contact with ISIS members in Syria, were detained in dawn raids in four districts of the Aegean coastal city of Izmir on Thursday, the state-run Anadolu news agency said.
It said they were accused of financing, recruiting and providing logistical support to the group.
The military killed two suspected ISIS members trying to enter Turkey illegally at the weekend, security sources said on Thursday.
One of the suspects, a Syrian national, was thought to have been plotting a suicide bomb attack in either the capital Ankara or the southern province of Adana, home to Incirlik, a major base used by U.S. and Turkish forces through which some coalition air strikes against ISIS are carried out.