A Turkish official has said three suspected Islamic State (IS) suicide bombers who attacked Istanbul’s Ataturk International Airport this week were from Russia, Uzbekistan, and Kyrgyzstan.

Authorities also announced the detention of 13 more people, including three foreign nationals, in connection with the June 28 gun-and-bomb attack that killed at least 43 people and injured more than 200 more.

The attack on Europe’s third-busiest airport was the deadliest in a series of suicide bombings in Turkey this year, and the latest of more than a dozen major attacks in that country in the past 12 months.

No group has claimed responsibility for the attack, but Ankara has blamed the IS militant group.

Russia’s ambassador to Turkey, Andrei Karlov, told journalists after the suspected perpetrators’ identities were leaked on June 30 that he had no information regarding the involvement of any Russian citizen in the attack.

“I do not have any information on that matter,” Karlov said.

Interfax quoted Russian law enforcement as disputing that one of those named had ever lived in Chechnya, as local media suggested.

A spokesman for Kyrgyzstan’s Interior Ministry, Ernis Osmonbaev, meanwhile told RFE/RL that the government was “investigating the reports.”

“At this point, we cannot say that our citizen was among [the attackers],” Osmonbaev said.

Uzbekistan’s security service could not immediately be reached for comment.

To varying degrees, all three of those post-Soviet states are said to be sources of IS recruits who have traveled to fight in the Middle East, where the group has declared a “caliphate” in swaths of conflict-torn Syria and Iraq.

INFOGRAPHIC: Foreign Fighters In Iraq & Syria — Where Do They Come From?

Russian officials say thousands of its citizens have fled to join the IS military effort in Syria — representing as much as around 10 percent of IS’s foreign fighting force. Russia has also battled a long-running Islamist-fueled insurgency in its North Caucasus region, including in Chechnya and Daghestan.

Kyrgyz authorities have reported thwarting a number of terrorist attacks in that predominantly Muslim country that they said were planned by IS members, and they have tried to crack down on alleged recruiters for the group.

Officials in Uzbekistan, which is also predominantly Muslim, have warned of IS recruiting efforts there not only for fighters but also targeting “specialists” including engineers and doctors. Authorities in Tashkent have estimated that many hundreds of Uzbek nationals have joined the fight alongside IS in Syria.

The Turkish official who was quoted by local and Western media as identifying the nationalities of the attackers on June 30 declined to be named because details of the investigation have not yet been released. He did not disclose any further details.

Links To North Caucasus

Investigators had been struggling to identify the bombers from their limited remains.

The pro-government Yeni Safak newspaper said the Russian bomber was from Daghestan, which borders restive Chechnya in Russia’s long-beleaguered North Caucasus region.

Yeni Safak said the suspected organizer of the attack was a man of Chechen origin called Akhmed Chatayev. Chatayev is identified on a United Nations sanctions list as an IS leader responsible for training Russian-speaking militants, and he is wanted by Russian authorities.

Turkey’s Hurriyet newspaper named one of the attackers as a Chechen, Osman Vadinov, and said he had come from Raqqa, the de facto capital of IS militants in Syria and Iraq.

But Interfax quoted Russian law enforcement as disputing anyone with that name had ever lived in Chechnya.

The Dogan news agency said the Russian attacker had entered Turkey one month ago and left his passport in a house the men had rented in the Istanbul neighborhood of Fatih.

The Karsi newspaper, quoting police sources, said the three suspected attackers were part of a seven-person cell who entered Turkey on May 25. The attackers raised the suspicion of airport security on the day of the attack because they showed up in winter jackets on a summer day, local media reported.

The Turkish government confirmed the attackers arrived at the airport by regular taxi. Hurriyet newspaper quoted sources as saying the taxi driver told the authorities the assailants spoke a foreign language.

Revelations of the suspects’ nationalities came shortly after Turkish police said they had detained three foreigners among 13 individuals being held in connection with the attack.

In separate large-scale police operations, nine suspects believed to be linked to IS were also detained in the coastal city of Izmir. It was not clear if those suspects had any links to the carnage at the airport.

NATO member Turkey shares long, porous borders with both Syria and Iraq. Ankara has blamed IS militants for several major bombings over the past year, including in the capital and against tourists in Istanbul.

Critics say Turkey woke up too late to the threat from IS militants, focusing instead on efforts to oust President Bashar al-Assad, arguing there could be no peace without his departure.

Ankara adjusted its military rules of engagement this month to allow NATO allies to carry out more patrol flights along its border with Syria.

With reporting by RFE/RL’s Kyrgyz, Russian, and Uzbek services, AP, Reuters, and Interfax