(CNN) It's happened again: another terror attack. The scene this time: Turkey's Istanbul Ataturk Airport, one of the busiest airports in Europe.
At least 42 people died and 239 were injured when three attackers armed with firearms and explosives arrived at the airport in a taxi Tuesday night, then opened fire before blowing themselves up, according to Turkish authorities.
Here's what you need to know about this developing story:
How the attack unfolded: The attackers opened fire with guns before detonating their bombs as security personnel tried to stop the assault. Two detonated their bombs at the airport's international terminal building, a third was killed in the nearby parking lot, a Turkish official told CNN. One video from the attack shows a man, apparently an attacker, running with a gun. He falls after apparently being shot by a security officer, who briefly stands over the man before running away. About 10 seconds later, an explosion goes off.
What witnesses saw: "It was like hell," said Mine Iyidinc. "There was panic everywhere. We did not understand that it was a terrorist attack." Witnesses reported feeling shock waves from the blasts and seeing broken glass everywhere. Another video from inside the airport shows some people slipping on the floor, which was covered in blood in some places.
How did the attackers pull it off? While the airport has plentiful security -- with checkpoints before entering the terminal building and again after passport control -- the attackers may have exploited relatively light security at the entrance to the arrivals hall, analysts say. Police have interviewed and released the taxi driver who drove the trio of attackers to the airport, according to the Anadolu news agency.
Who were the victims? Turkish authorities say 37 of the victims have been identified. At least 13 are foreigners, the government said. Among them: Two Iraqis, a Tunisian, a Chinese citizen, a Ukrainian, a Jordanian and a citizen of Uzbekistan, a Turkish official told CNN. Saudi Arabia said six of its citizens had died and five were still unaccounted for. The Palestian Authority's Foreign Ministry said a Palestinian was among the dead. Three of the foreigners have dual Turkish citizenship, the official said. Of the 239 injured, 128 people were still being treated in hospitals. Families of 19 people killed in the attack have already received the remains of their loved ones. One of the victims who was killed was airport worker, Ozgul Ide, whose death was announced by her alma mater, Istanbul Arel University.
There's no claim of responsibility yet. But there's also no shortage of suspects. Topping the list: ISIS, which has threatened Turkey over its involvement in the effort to eviscerate the terror group. Also possible: the PKK, a Kurdish separatist group labeled a terrorist organization by Turkey, the United States and others. Turkish officials seem to be leaning toward ISIS, with a senior Turkish government source telling CNN that while the bombers have not yet been identified, there's a "strong suggestion they are foreign." Analysts also say the style of the attack and the target point more toward ISIS.
Ataturk is already up and running again: The airport, the 11th busiest in the world, was closed for several hours overnight. Flights were diverted to Ankara, Turkey, and other cities. But it reopened at 2:20 a.m. Wednesday. Flights have resumed, although Iran canceled all scheduled flights between Tehran and Istanbul, Iran's semi-official Tasnim News Agency reported. Some forensic experts believe the airport may have contaminated evidence by reopening too soon.
It will be an official day of mourning in Turkey. The government declared the observation and said flags will be flown at half-staff in honor of the dead.
World reaction is pouring in. President Barack Obama spoke with Turkish President Recep Tayyip Erdogan on Wednesday, offering his condolences and U.S. support. U.K. Prime Minister David Cameron called Erdogan to say the UK stands with Turkey "as one in our defiance against these barbaric acts." Russian President Vladimir Putin -- who's ordered a rapprochement with Turkey -- also offered his condolences and said the attack "confirms the need for a joint fight against terrorism." Pope Francis prayed for the victims and U.N. Secretary-General Ban Ki-moon said more efforts are needed to combat terror. And all around the world, buildings were lit up in the colors of the Turkish flag -- red and white.
Erdogan's strong words: The President said the terror attack on travelers and workers at Istanbul's airport "will not divide or split our country." Erdogan said, "We will be among the top 10 business countries in the world. This is why they want to divide us, because they cannot take our growing power." He promised the government will "not let down our people" and said the attackers didn't act in an Islamic way. "Taking one person's life means going straight to hell," he said.
This is just the latest in a string of terror attacks in Turkey this year. Terrorists have struck Turkey seven other times in 2016, hitting tourist sites and police targets with deadly effect. So far, at least 140 people have died in such attacks.
The attack could push Turkey deeper into the fight against ISIS. "I would expect that Turkey's vengeance will come down like rain from hell," Soner Cagaptay of the Turkish Research Program at the Washington Institute told CNN. "For Turkey now, fighting the so-called Islamic State is going to be priority number one."