Turkish security experts piecing together the evidence of Tuesday night's attack on Istanbul's Ataturk Airport agree: The carefully planned and methodically executed assault on the very hub of Turkey's commercial capital was the work of Islamic State, the radical Sunni movement that has established a self-declared "caliphate" on large parts of Iraq and Syria and wants very much to expand its fight into Turkey.
For this, the security people also agree, Turkey will make them pay.
"Turkey's vengeance will come down like rain from hell," said Soner Cagaptay, director of the Turkish research program at the Washington Institute for Near East Policy. Until now, "Turkey has avoided engaging Islamic State in full war," he said, despite some 16 terror attacks in Turkey in the past 12 months. "Not any longer."
Tuesday's triple-suicide assault claimed the lives of more than 40 people and the final number may grow, since almost a quarter of the more than 230 people injured in the attack remain in intensive care in Istanbul hospitals.
Pointing the finger at Islamic State, Turkish President Recep Tayyip Erdogan declared it a turning point in the global fight against terrorism. The airport attackers were "not Muslims," he said at a Ramadan fast-breaking meal on Wednesday evening. They "have prepared their place in hell."
A day after the attack, Reuters reported, broken ceiling panels littered the curb outside the arrivals section of the international terminal. Plates of glass had shattered, exposing the inside of the building, and electric cables dangled from the ceiling.
Cleanup crews swept up debris as delayed travellers slept on floors. Police in Kevlar vests with automatic weapons prowled the curbside as a handful of travellers and Turkish Airlines crew members trickled in. The national carrier said it had cancelled 340 flights, although its departures resumed just after 8 a.m. on Wednesday, less than 12 hours after the deadly attack.
Thirteen foreigners were killed, including five Saudis, two Iraqis and citizens from China, Jordan, Tunisia, Uzbekistan, Iran and Ukraine.
One attacker opened fire in the departures hall with an automatic rifle, sending passengers diving for cover and trying to flee, witnesses said. Two other explosions hit the arrivals floor below, one of them just outside the building. Video footage showed one attacker inside the terminal being shot, apparently by a police officer, before falling to the ground as people scattered. The attacker then blew himself up about 20 seconds later.
The attack bore similarities to a suicide bombing by Islamic State militants at Brussels Airport in March that killed 16 people. A co-ordinated attack also targeted a rush-hour metro train, killing a further 16 people in the Belgian capital.
The European airports association, ACI Europe, said airport security had been stepped up across the continent after the Brussels attacks, but said many of the fatalities in Istanbul came as people queued for security checks at the entrance.
"We must face the reality that when dealing with a terror threat based on suicide bombing, no security measures can ensure 100-per-cent protection," the group said.
Turkey has no choice but to attack Islamic State, Mr. Cagaptay said. "I would expect there will be an increase in the number of Turkish air strikes as part of the U.S.-led coalition inside Syria."
He added: "I also expect there to be increased co-operation with the U.S. to seal the Turkish-Syrian border, and deeper co-operation with Western intelligence agencies to track the perpetrators of the attack and prevent future ones."
Whether Turkey will launch independent attacks – by air or on the ground – on Islamic State centres in Syria "will depend very much on Russia," Mr. Cagaptay said. "Russia controls much of Syria's airspace" and has been especially vigilant about any Turkish fighters entering the area ever since Turkey shot down a Russian fighter jet bombing rebel Turkmen fighters near the border with Turkey in November.
Fortunately for Turkey, Mr. Cagaptay noted, Mr. Erdogan sent a letter on Monday to Russian President Vladimir Putin apologizing for the downing of the Russian jet seven months ago. Mr. Putin responded quickly. On Tuesday, he ordered the lifting of a ban on Russians travelling to Turkey, much to the relief of the Turkish tourism industry.
The two leaders reportedly spoke by telephone on Wednesday, with Mr. Putin pledging support for what is expected to be a fierce campaign against IS militants by Turkey. Israeli Prime Minister Benjamin Netanyahu also called on "all civilized nations" to "fight the scourge of terrorism," a reflection of the renewed relations between Israel and Turkey since their reconciliation earlier this week.
Metin Gurcan, a former Turkish military adviser who is now an independent security analyst, noted that Islamic State seems determined to open a front in Turkey, forcing Ankara to respond in kind to the group's military actions.
Islamic State is "under increasing pressure in Syria and Iraq," he said Wednesday. Launching attacks by "semi-autonomous networks" of IS followers will keep authorities busy. The decentralization of deciding on place and timing of attacks "makes detection and prevention much more difficult for security forces."
As well, Mr. Gurcan pointed out, when Turkish security and intelligence bodies strive to cope with these serious developments, they "will also be subject to public criticism, which may trigger even harsher countermeasures."
For more than a year, Mr. Gurcan wrote recently, "Turkey has been arresting a growing number of IS militants and sympathizers, but Ankara, aware of local sensitivities, has been careful to keep its anti-IS struggle inside Turkey low-key without attracting media attention and upsetting public opinion."
After this week's attack on Istanbul's airport, the government's actions will be anything but low-key.
With a report from Reuters