ISTANBUL, Turkey -- Turkish authorities have now detained 22 people in connection with the Ataturk Airport attack, a Turkish official told CNN on Thursday.
Thirteen people were taken into custody in Istanbul and nine in the coastal city of Izmir, the official said. Three of those detained were foreign nationals, state media reported.
The official also said that Turkey has determined the attackers who carried out Tuesday's shootings and suicide bombings were from Russia, Uzbekistan, and Kyrgyzstan.
No one has claimed responsibility for the attack that hit one of Europe's busiest transit hubs.
Three terrorists stormed the airport Tuesday night, opening fire and detonating explosives in an attack that killed 42 people and wounded hundreds more.
When the attackers arrived at the Turkish airport armed with rifles and suicide bomb vests, two opened fire and detonated their bombs at the international terminal building, according to officials.
A third one died in the parking lot, where he detonated himself as terrified travelers scattered in all directions.
The attack echoed the dual suicide bombings at the main airport in Brussels in March.
Like the attack in Brussels, the terrorists took a taxi to the airport.
After the terror attack, police interviewed the taxi driver who drove the Istanbul terrorists to the airport and released him, Turkish state news agency Anadolu reported.
'All evidence' points to ISIS
As Turkey flew flags at half-staff to observe a day of mourning Wednesday, questions remained on who was behind the attack.
President Recep Tayyip Erdogan proclaimed the terror attack "will not divide or split our country." Officials blamed the attack on ISIS, the abhorred terror group based in neighboring Syria.
By killing dozens of civilians, including women and children, Erdogan said, the terrorists are not true Muslims.
"This is not Islamic. Taking one person's life means going straight to hell," he said. "No terrorist organization will come between what we are."
Erdogan said an attack during the final days of the holy month of Ramadan shows the terrorists had no regard for faith or values.
"All information and evidence" points to ISIS, Interior Minister Efkan Ala said. "But nothing is for certain."
The Islamic State has struck in Turkey before, but has rarely taken credit for those bombings.
History of airport attacks
Preliminary findings suggest all three attackers opened fire then detonated themselves, similar to the mass shooting and suicide bombings at Paris' Bataclan concert hall in November. ISIS claimed responsibility for that massacre, which left 89 people dead.
ISIS has a history of airport attacks. It also claimed responsibility for dual suicide bombings at the main airport in Brussels in March. At least 10 people died in those blasts.
The CIA director said the terror attack mirrors similar ones by ISIS.
"I think what they do is they carry out these attacks to gain the benefits from it in terms of sending a signal to our Turkish partners ... and at the same time not wanting to potentially maybe alienate some of those individuals inside of Turkey that they may still be trying to gain the support of," John Brennan said.
Victims from all over the world
The people killed came from all over the world, but most of them were Turkish, including 10 airport staff members, TAV Airports CEO Sani Sener said.
The attack killed six Saudis and wounded dozens more, the nation's foreign ministry said.
Other fatalities included two Iraqis, one Tunisian, one Chinese, one Iranian, one Ukrainian, one Jordanian and one person from Uzbekistan, a Turkish official said. Three of the foreigners had dual Turkish citizenship.
Of the 239 people wounded, a majority of them remained hospitalized, officials said.
Experts say Turkey is especially vulnerable because various terrorists operate there.
ISIS has a reason to detest Turkey. The country is helping the U.S.-led coalition attack ISIS targets in neighboring Iraq and Syria. Turkey allows coalition planes to fly raids from its territory.
Adding to the list of enemies, Turkey resumed hostilities with the PKK -- Kurdish militant separatists -- last year after a ceasefire broke down.
Turkey has spent much of this year reeling from terror attacks as it weathers bombing campaigns by both ISIS and Kurdish militants.
The attack marked the eighth suicide bombing in Turkey this year. At least 140 people have been killed. The violence has also rattled Turkey's tourism industry, a key sector of the national economy. About 39.4 million people visit each year.
The airport resumed flights Wednesday morning, hours after the attack.
A few shops inside the airport remained closed, but for the most part the terminal where the attack took place was open. A section where one of the bombs went off was cordoned off by boards with advertisements on them.
Not too far away, a black table sat covered with roses and a photo of two victims.
CNN's Gul Tuysuz reported from Istanbul; CNN's Faith Karimi and Steve Almasy reported and wrote from Atlanta.