ISTANBUL -- Several suicide bombers have hit Istanbul's Ataturk airport, killing at least 36 people and injuring dozens more, Turkey's prime minister says.
Turkish Prime Minister Binali Yildirim said 36 were dead and Justice Minister Bekir Bozdag said 147 were wounded. Another senior government official told The Associated Press the death toll could climb much higher.
Yildirim says that so far all indications point to the Islamic State of Iraq and Syria (ISIS) being behind the attack. He says the attackers arrived at the airport in a taxi and blew themselves up after opening fire.
Asked whether a fourth attacker might have escaped, he says authorities have no such assessment but are considering every possibility.
Yildirim says the victims include some foreigners and that many of the dozens wounded have minor injuries but others are more badly hurt. He says the attacks come as Turkey is having success in fighting terrorism and trying to normalize ties with neighbors like Russia and Israel.
Flight operations at the airport were halted for many hours after the attacks but were resuming Wednesday, Turkish Airlines said on its website.
Saudi Arabia's Embassy in Turkey says at least seven Saudis were injured in the attack and all are in stable condition.
The embassy statement was carried on Saudi Arabia's state-owned al-Ekhbaria news channel early Wednesday. Muslim-majority Turkey is a popular tourist destination for Arabs from the Gulf, particularly during the summer.
CBS News senior investigative producer Pat Milton reports that a U.S. law enforcement source said while there still has been no claims of responsibility, authorities are leaning towards this being an ISIS attack.
The source said the tactics, methodology-multiple attackers, shootings and detonating explosives causes them to lean towards ISIS. But the source said nothing is definitive, especially given that Kurdish terrorists have attacked in the past.
Authorities are seeking the identities of the terrorists and combing the airport for other possible planted devices.
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.
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.
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 said on Twitter they are working to determine if U.S. citizens are among the victims.
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.
U.N. Secretary-General Ban Ki-moon has also condemned the "terrorist attack," and is calling for the perpetrators to be identified and brought to justice.
U.N. deputy spokesman Farhan Haq said the secretary-general "stands firmly by Turkey as it confronts this threat and stresses the need to intensify regional and international efforts to combat terrorism and violent extremism."
Mogens Lykketoft, president of the 193-member U.N. General Assembly, expressed anger and grief at the attack.
"Once again we experience the senseless killing of innocent and peaceful civilians," he said. "The international community must -- through much closer cooperation -- redouble efforts to contain and fight radical and violent extremism."
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 were among those around the U.S. 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.
The Department of Homeland Security said in a statement that it "continues to closely monitor the events at the Istanbul Atatürk Airport."
Secretary Jeh Johnson has been briefed on the situation, and is directing appropriate actions as the facts warrant. DHS is also in contact with its domestic, international and private sector counterparts, CBS News transportaion correspondent Kris Van Cleave reported.
European Union leaders holding an unprecedented summit about Britain's departure from the bloc joined those 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."
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."
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.
"Suddenly, there was just sort of layers of shooting and then an incredibly loud bang, which I presume must have been the bomb that went off," Favish told CBSN. "And then I ran for shelter beneath one of the counters and stayed there for about ten minutes."
Favish said passengers were ushered to a cafeteria on the basement level where they were kept for more than an hour before being allowed outside. Some of the travelers were having panic attacks and at least one man and one woman had been shot, Favish said.
"Coming out, two hours later, there was blood everywhere," she said. "One of the little rooms had been shattered. It was horrible. It was just horrible -- chaos and blood and people running around and anxious worried, and it was just horrible."
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.
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 the attack had 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, but they later lifted that restriction.
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.
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.