Several suicide bombers have hit Istanbul's Ataturk airport, killing at least 31 people and injuring some 147 more, Turkey's Justice Minister Bekir Bozdag says.
Another senior government official says the death toll could climb much higher.
Turkey's NTV television quoted Istanbul Governor Vasip Sahin as saying three suicide bombers carried out the attack.
A U.S. source tells CBS Radio News that three attackers approached the departure area at the Istanbul airport, threw four grenades, then opened fire with automatic weapons. They were wounded by Turkish security forces. The assailants then detonated the suicide vests.
Bozdag earlier said that according to preliminary information, "a terrorist at the international terminal entrance first opened fire with a Kalashnikov and then blew himself up."
Another official said attackers detonated explosives at the entrance of the international terminal after police fired at them.
The official, who spoke on condition of anonymity in line with government protocol, said the attackers blew themselves up before entering the x-ray security check at the airport entrance.
Turkish airports have security checks at both at the entrance of terminal buildings and then later before entry to departure gates. Roads around the airport were sealed off for regular traffic after the attack and several ambulances could be seen driving back and forth.
A Turkish official says the "vast majority'" of causalities in the airport attack were Turkish, but some foreigners, Reuters reports.
Hundreds of passengers were spilling out of the airport with their suitcases in hand or stacked onto trolleys. Others were sitting on the grass, their bodies lit by the flashing lights of ambulances and police cars.
Turkish President Recep Tayyip Erdogan released a statement condemning the attack, which took place during the Muslim holy month of Ramadan. He says the attack "shows that terrorism strikes with no regard to faith and values."
He has called on the international community to take a firm stand against terrorism and vowed to keep up Turkey's struggle against terror groups.
Erdogan says "Turkey has the power, determination and capacity to continue the fight against terrorism until the end."
The U.S. State Department confirmed the explosions on Twitter, saying they are working to determine if U.S. citizens are among the victims.
US Consulate working to determine if US citizens are among victims in #Turkey. Updates forthcoming.— Travel - State Dept (@TravelGov) June 28, 2016
Confirming reports of two explosions and gunfire at Istanbul Ataturk airport in #Turkey.— Travel - State Dept (@TravelGov) June 28, 2016
A White House official tells CBS News that the president has been briefed on the explosions.
White House press secretary Josh Earnest released a statement condemning the attack.
"Ataturk International Airport, like Brussels Airport which was attacked earlier this year, is a symbol of international connections and the ties that bind us together," the statement read.
A DOJ spokesperson tells CBS News justice reporter Paula Reid that the Attorney General has been briefed on the explosions. The Justice Department and the FBI are coordinating with other U.S. Government agencies, and have offered assistance to our Turkish counterparts as needed.
New York City-area airports are making security adjustments following the attack.
"In the wake of today's tragic attack on the Istanbul airport, Port Authority police have added high visibility patrols equipped with tactical weapons and equipment at Kennedy, LaGuardia and Newark Liberty airports," the Port Authority said in a statement.
European Union leaders holding an unprecedented summit about Britain's departure from the bloc are condemning the deadly attack.
Belgian Prime Minister Charles Michel tweeted from a closed-door meeting Tuesday in Brussels, "Despicable terror attack. Stand together with people of Turkey."
Our thoughts are with the victims of the attacks at Istanbul's airport. We condemn these atrocious acts of violence #Istanbul— Charles Michel (@CharlesMichel) June 28, 2016
Dalia Grybauskaite, president of Lithuania, wrote "Our thoughts are with the victims of the attacks at Istanbul airport. We condemn those atrocious acts of violence."
Two South African tourists, Paul and Susie Roos from Cape Town, were at the airport and due to fly home at the time of the explosions and were shaken by what they witnessed.
"We came up from the arrivals to the departures, up the escalator when we heard these shots going off," Paul Roos said. "There was this guy going roaming around, he was dressed in black and he had a hand gun."
Twelve-year-old Hevin Zini had just arrived from Dusseldorf with her family and was in tears from the shock.
She tells The Associated Press that there was blood on the ground and everything was blown up to bits.
South African Judy Favish, who spent two days in Istanbul as a layover on her way home from Dublin, had just checked in when she heard an explosion followed by gunfire and a loud bang.
She says she hid under the counter for some time.
Favish says passengers were ushered to a cafeteria at the basement level where they were kept for more than an hour before being allowed outside.
Taxis were ferrying wounded people from the airport. The private DHA news agency said the wounded, among them police officers, were being transferred to Bakirkoy State Hospital.
The FAA said in a statement that is has put in place a ground stop for any U.S. flights departing for Istanbul, and any flights leaving Istanbul for the U.S. as well.
Turkey has suffered several bombings in recent months linked to Kurdish or Islamic State of Iraq and Syria (ISIS) militants.
The attacks have increased in scale and frequency, scaring off tourists and hurting the economy, which relies heavily on tourism revenues.
A Senior Turkish official says initial indications suggest ISIS is behind the airport attack.
However, a U.S. official tells CBS News homeland security correspondent Jeff Pegues that it is too early to attribute responsibility for the explosions at the airport. But a U.S. official says two organizations come to mind at the top of the list: ISIS and the PKK (The Kurdistan Workers Party).
"The initial reaction is it is potentially Kurdish groups who have been amplifying their attacks...on the other hand, this also follows an Islamic State MO," Senior national security analyst Juan Zarate said on CBSN.
In December, a blast at Istanbul's Sabiha Gokcen killed one person and wounded another. Both were cleaners. Kurdish rebels later claimed responsibility for the explosion, believed to have been caused by a bomb.
Istanbul's Ataturk Airport was the 11th busiest airport in the world last year, with 61.8 million passengers, according to Airports Council International. It is also one of the fastest-growing airports in the world, seeing 9.2 percent more passengers last year than in 2014.
The largest carrier at the airport is Turkish Airlines, which operates a major hub there. Low-cost Turkish carrier Onur Air is the second-largest airline there.