Authorities blamed the Islamic State for the blood bath late Tuesday, a coordinated assault on one of the world's busiest airports and on a key NATO ally that plays a crucial role in the fight against the extremist group.
There was no immediate claim of responsibility by the militant group.
Although the attack took a heavy toll, the assailants were initially thwarted by the extensive security on the airport's perimeter, Turkish officials said.
"When the terrorists couldn't pass the regular security system, when they couldn't pass the scanners, police and security controls, they returned and took their weapons out of their suitcases and opened fire at random at the security check," Turkish Prime Minister Binali Yildirim said.
WARNING: Dramatic Video reportedly shows explosion inside Istanbul airport
One attacker detonated his explosives downstairs at the arrivals terminal, one went upstairs and blew himself up in the departure hall, and the third waited outside for the fleeing crowd and caused the final lethal blast, two Turkish officials said, speaking on condition of anonymity because they weren't authorized to speak about the investigation publicly. None of the attackers were Turks, a third official said.
As the chaos unfolded, terrified travelers were sent running first from one explosion and then another. Airport surveillance video showed a panicked crowd of people, some rolling suitcases behind them, stampeding down a corridor, looking fearfully over their shoulders.
Other surveillance footage posted on social media showed one explosion, a ball of fire that sent terrified passengers racing for cover. Another showed an attacker, felled by a gunshot from a security officer, blowing himself up seconds later.
Cihan Tunctas had just disembarked from a flight from Azerbaijan when he heard the sound of gunfire.
"Then the bomb exploded. We were at the exit and ... the roof collapsed on our heads," Tunctas said. The group tried to escape, but their path was blocked by the arrival of a second attacker.
"Two of the security guards noticed him. They walked toward him. Just as they were walking toward him, I turned that way. They just caught him and at that moment he detonated the bomb."
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Investigators later found a Kalashnikov assault rifle, a handgun and two grenades on the bodies, according to the state-run Anadolu news service. Raids at two addresses also uncovered encrypted organizational documents and computer files, the news agency said.
Although the government quickly blamed the Islamic State, there was no immediate claim of responsibility by the extremist group, which did not mention the bloodshed on its social media sites Wednesday. However, an infographic released to celebrate the second anniversary of its self-proclaimed caliphate claimed to have "covert units" in Turkey and other countries.
Islamic State, however, rarely claims attacks in Turkey. One possible reason is a reluctance to be seen as killing fellow Muslims, said Anthony Skinner, director of the analyst group Verisk Maplecroft. Another is its desire to exploit the violent rift between Turkey and Kurdish rebels, he said.
"It very clearly meets Islamic State's strategic objectives to leave this ambiguity," Skinner said.
Yildirim, the Turkish prime minister, also suggested the attack could be linked to steps Ankara took Monday toward mending strained ties with Israel and Russia. Late Wednesday, he told the Turkish public the authorities were increasingly convinced that the Islamic State group, also known as Daesh, was responsible for the ghastly attack.
"Our thought that it is Daesh, continues to gain weight," Yildirim said.
A key partner in the U.S.-led coalition against the Islamic State group, Turkey faces an array of security threats from other groups as well, including ultra-left radicals and Kurdish rebels demanding greater autonomy in the restive southeast.
The country shares long, porous borders with both Syria and Iraq, where IS controls large pockets of territory, and the government has blamed IS for several major bombings over the past year, including in the capital Ankara, and on tourists in Istanbul.
"The reality is that Turkey is situated in a very vulnerable situation, geographically speaking," Skinner said.
Victims in Tuesday's attack included at least 13 foreigners and several people remained unidentified Wednesday. The Istanbul governor's office said more than 230 people were wounded and dozens remained in critical condition.
Among the dead was Muhammed Eymen Demirci, who had just landed a job on the airport's ground services crew after more than a year of unemployment: "I got the job bro!" the 25-year-old texted a friend in May.
He died while waiting for a bus after his shift. A childhood friend who had helped Demirci get the job was devastated. "He was such a friendly person, a man who fought for his ideals," Deniz Dogan told The Associated Press. "Now I wish he hadn't gotten the job."
"So, what can we think? We cannot think anything," said Ali Batur, whose brother also died. "A terror attack might happen everywhere, it does happen everywhere."
Dozens of anxious friends and relatives waited Wednesday outside Istanbul's Bakirkoy Hospital.
"You can hear that people are wailing here," said Serdar Tatlisu, a relative of a victim. "We cannot cope anymore, we can't just stay still. We need some kind of solution for whatever problem there is."
Funerals for some of the victims began Wednesday as Turkish authorities sought to put together an attack timeline, going through surveillance footage and interviewing witnesses. A Turkish court imposed a media ban on any information not officially released by the government.
The devastation at Istanbul's airport was a reminder of the March 22 attack on the Brussels airport, where two suicide bombings ripped through check-in counters, killing 16 people. The Islamic State group claimed responsibility for that attack, as well as an explosion the same day at a Brussels subway station that killed 16 more people.
As dawn broke Wednesday, workers were removing debris from the Istanbul airport and mere hours after the terminal erupted into chaos, it reopened to flights. It took 12 days for flights to resume in Brussels, and more than two months for the terminal building to fully reopen.
Turkey has suffered a series of attacks that have frightened away visitors and devastated its economy, which relies heavily on tourism.
The government has stepped up controls at airports and land borders and deported thousands of foreign fighters, but has struggled to tackle the extremist threat while also conducting security operations against Kurdish rebels. Turkish airports have security checks at both the entrances to terminal buildings and before the entrances to departure gates.
This year alone, a Jan. 12 attack that Turkish authorities blamed on IS claimed the lives of a dozen German tourists visiting Istanbul's historic sites. On March 19, a suicide bombing rocked Istanbul's main pedestrian street, killing five people, including the bomber, whom the authorities identified as a Turkish national linked to IS.
Last October, twin suicide bombings hit a peace rally outside Ankara's train station, killing 103 people. There was no claim of responsibility but Turkish authorities blamed it on an Islamic State cell.
Fraser reported from Ankara. Zeynep Bilginsoy in Istanbul; Lori Hinnant in Paris; Bram Janssen in Istanbul, Desmond Butler in Washington, D.C. and Scott Mayerowitz in New York contributed.