At least two explosions rocked the international airport in Istanbul, Turkey, on Tuesday night, killing at least 10 people and wounding dozens more, officials said.
Officials could not immediately say whether the blasts were caused by bombs or a suicide attack.
Deputy of Istanbul Eren Erdem said on Twitter that 10 people were dead and at least 20 were injured. The U.S. State Department said it was working to determine if any Americans were among the victims.
The blasts occurred at the international arrivals area at Ataturk International Airport, a busy terminal where people come from all over the world.
A person who works for a contractor inside the airport told NBC News that he saw three suicide bombers.
The man, who identified himself as Omar, said he heard an explosion and then saw police jump on a man who then blew himself up. People then tried to stop another person who appeared to be wearing explosives.
Another witness gave a similar account to NBC News, and said he heard a third explosion outside.
One witness told national broadcaster TRT that he saw two attackers open fire and then blow themselves up as authorities responded at a security checkpoint outside the international terminal. At least one of the gunmen was armed with an AK-47, TRT said, quoting the justice minister.
The account could not be immediately confirmed by NBC News.
Video posted to social media purports to show travelers hiding in a store inside the airport amid the chaos:
Turkish media reported the sound of gunfire, and video from the scene showed ambulances racing to the terminal and people yelling.
“Passengers (were) running everywhere, scurrying. I was hiding,” a witness told TRT.
Turkey has historically suffered attacks from Kurdish separatists, although ISIS has in recent months stepped up bombings in the country.
There was no immediate claim of responsibility for the attack in Istanbul, but rebels of the Kurdistan Workers’ Party, or PKK, have been targeting police and military personnel with bombs since last July, when a fragile peace process between the rebels and the government collapsed.
Experts say ISIS is likely behind the blasts. The terror group in March took responsibility for the attack at the Brussels airport, killing 32 people. Two suicide bombers attacked the departure hall before a metro station was also bombed.
A senior U.S. counterterrorism official told NBC News the Istanbul attack “fits the ISIS profile, not PKK.”
“There are only two groups capable of carrying out such a large-scale attack. This does not fit the PKK profile, they go after Turkish targets, not international targets,” the official said.
The official was unaware of any “chatter” that threatened an attack, but there remains a “heightened state of alert” throughout Europe for months.
On Monday, the U.S. State Department had issued a revised warning to U.S. citizens advising of “increased threats from terrorist groups throughout Turkey.”
Earlier this month, a car bomb attack targeting a bus carrying Turkish police killed 11 people. Thirty-six others were wounded in the attack, Istanbul officials said.
Other bombings have included two in Istanbul targeting tourists — which authorities have blamed on ISIS.
The attacks have increased in scale and frequency, scaring off tourists and hurting the economy, which relies heavily on tourism revenues.
This is a breaking news story. Please check back for updates.