Explosions Rock Istanbul Airport

ISTANBUL — Explosions rocked Turkey's largest airport Tuesday night, killing at least three dozen people and wounding scores more in what appeared to be a coordinated terror attack, officials said.

The gunmen opened fire around 10:30 p.m. local time (3:30 p.m. ET) at the entrance of the international arrivals area at Ataturk International Airport in Istanbul, where detonated explosives sent people running for their lives, witnesses and officials said.

The number of dead and injured fluctuated steadily overnight amid the confusion, and Prime Minister Binali Yildirim said on television that at least 36 people were killed.

The Turkish Red Crescent counted "over a hundred" injured.

"I call on every citizen to act in unity and stand by each other, and I believe that this is going to be the best answer to the terrorists," Yildirim said. Initial indications are that ISIS carried out the killings, he added, "but we are still working on determining the cause."

The White House condemned the blasts as a "heinous terrorist attack," and the U.S. State Department said it was determining if any victims were American.

The attackers arrived at the airport in a cab, Yildirim said. At least two blasts occurred at a checkpoint at a busy terminal that serves as a major hub, particularly for people traveling between Europe and Asia.

In the aftermath of the explosions, U.S. carriers were halted from flying directly into Turkey — a country that has become the main transit point for foreign fighters in and out of Syria, where ISIS controls part of the country.

A person who works for a contractor inside the airport told NBC News that he saw three suicide bombers.

Another witness said he heard the first blast at a parking lot, where the attacker had an AK-47 and started shooting before blowing himself up. That drew security to the scene.

Meanwhile, another person at the international arrivals area blew himself up, creating more confusion. A third attacker then got inside the greeting point at a kiosk at the terminal.

That attacker was noticed by police, who started yelling, "suicide bomber," but they were unable to stop another explosion, a witness told NBC News.

A porter who works at the airport gave a similar account to NBC News, and said he heard a third explosion outside. Closed circuit TV that appears to be from the scene purportedly showed one of the attackers slip to the ground, drop an object and then blow himself up.