ISTANBUL -- Suicide attackers killed dozens and wounded more than 140 at Istanbul's busy Ataturk Airport, andTurkish officials blamed Tuesday's massacre at the international terminal on three militants with suspected ties to ISIS (the Islamic State of Iraq and Syria).
The Istanbul governor's office said 41 people were dead, among them 13 foreigners, including three dual-nationals. It said more than 230 people were wounded.
Another senior government official told The Associated Press the death toll could climb much higher. The senior official, who spoke on condition of anonymity in line with government protocol, at first said close to 50 people had already died, but later said that the figure was expected to rise to close to 50.
Hundreds of frightened passengers streamed out of the airport, fleeing the latest of several bombings to strike Turkey in recent months. The attacks on a key partner in the U.S.-led coalition against ISIS and a NATO member have increased in scale and frequency. They have scared off tourists and hurt the Turkish economy, which relies heavily on tourism.
Officials began assessing the damage Wednesday morning. Workers were brought in to remove debris left by the blast, while in the daylight the damage to the terminal became clearer -- even ceiling panels had been hit.
Yildirim, speaking to reporters at the airport, said all initial indications suggested ISIS was behind the attack.
"The findings of our security forces point at the Daesh organization as the perpetrators of this terror attack," Yildirim said, using the Arabic name for ISIS. "Even though the indications suggest Daesh, our investigations are continuing."
CBS News senior investigative producer Pat Milton reports that a U.S. law enforcement source said authorities are leaning toward this having been an ISIS attack.
The source said the tactics, methodology-multiple attackers, shootings and detonating explosives cause them to lean toward ISIS. But the source said nothing is definitive, especially given that Kurdish separatists have attacked in the past.
U.S. Secretary of State John Kerry said the fact that ISIS could be the culprit in another airport attack is a sign of weakness.
Speaking Tuesday evening at the Aspen Ideas Festival in Colorado, Kerry said, "It has been more than one year since Daesh has actually launched a full scale military offensive, and that's because our coalition is moving relentlessly on every front. ... Now, yes, you can bomb an airport, you can blow yourself up. That's the tragedy. ... And if you're desperate and if you know you are losing, and you know you want to give up your life, then obviously you can do some harm. ... We are still collecting information and trying to ascertain what happened and who did it."
Passengers described scenes of carnage.
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.
Favish told CBSN passengers were ushered to a cafeteria on the basement level and kept there for more than an hour before being allowed outside.
"Coming out ... 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."
Turkey shares long, porous borders with Syria and Iraq, war-torn countries where ISIS controls large pockets of territory. Authorities have blamed ISIS for several major bombings over the past year, including on the capital Ankara, as well as attacks on tourists in Istanbul.
In the wake of the Istanbul assault, additional security was being rolled out in numerous U.S. airports, among them those in the New York and Miami metropolitan areas.
Turkey has stepped up controls at airports and land borders and deported thousands of foreign fighters, but has struggled to tackle the threat of ISIS militants while also conducting vast security operations against Kurdish rebels, who have also been blamed for recent deadly attacks.
The devastation at Istanbul's airport follows the March attack on Brussels Airport, where two suicide bombings ripped through check-in counters, killing 16 people. ISIS claimed responsibility for that attack, as well as a subsequent explosion at a Brussels subway station that killed 16 more people.
Yildirim said air traffic at Ataturk Airport, which was suspended after the attack, had resumed and was back to normal early Wednesday, though the information board inside the airport showed that about a third of scheduled flights have been canceled and a host of others delayed.
A stoppage of flights to and from the United States and Istanbul lasted several hours but was later lifted, said a U.S. official who spoke on background in order to discuss sensitive security issues.
Yildirim said 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 said authorities have no such assessment but are considering every possibility.
Another Turkish official said two of the attackers detonated explosives at the entrance of the international arrivals terminal after police fired at them, while the third blew himself up in the parking lot.
The official, who also spoke on condition of anonymity in line with government regulations, cited interior ministry information and said that none of the attackers managed to get past security checks at the terminal's entrance.
Turkish airports have security checks at both 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. Passengers were left sitting on the grass outside the airport.
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.
"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."
The prime minister called for national unity and "global cooperation" in combatting terrorism.
"This (attack) has shown once again that terrorism is a global threat," Yildirim said. "This is a heinous planned attack that targeted innocent people."
He suggested that the attack was linked to what he said was Turkey's success against Kurdish rebels, as well as steps Ankara took Monday toward mending strained ties with Israel and Russia.
"It is meaningful that this heinous attack came at a time when we have become successful in the fight against separatist terrorism ... and at a time when we started a process of normalizing ties with our neighbors," Yildirim said.
Yildirim said there was no security lapse at the airport, but added the fact the attackers were carrying weapons "increased the severity" of the attack.
The victims included some foreigners, he said, adding that many of the wounded have minor injuries but others were more badly hurt.
The independent DHA news agency said the wounded, among them police officers, were transferred to Bakirkoy State Hospital.
Turkey is beset by a wide array of security threats, including from ultra-left radicals, Kurdish rebels demanding greater autonomy in the restive southeast, and ISIS militants.
On Jan. 12, an attack that Turkish authorities blamed on ISIS claimed the lives of a dozen German tourists visiting Istanbul's historic sites. On March 19, a suicide bombing rocked Istanbul's main pedestrian street, killing five people, including the bomber, whom the authorities identified as a Turkish national linked to ISIS.
Last October, twin suicide bombings hit a peace rally outside Ankara's train station, killing 102 people. There was no claim of responsibility but Turkish authorities blamed the attack on a local ISIS cell.
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.