Two explosions have rocked Istanbul's Ataturk airport, killing as many as 28 people and wounding many more.
Turkey's NTV channel has quoted the Istanbul governor saying the suicide attack killed 28 people and may have involved three suicide bombers.
The state-run Anadolu Agency is reporting 60 people have been injured, six of them seriously.
Turkey's justice minister Bekir Bozdag says, according to preliminary information, "a terrorist at the international terminal entrance first opened fire with a Kalashnikov and then blew himself up."
An NBC News reporter said on Twitter an eyewitness saw a police officer wrestling one of the suicide bombers to the ground before he detonated his bomb.
Another official said two attackers had detonated explosives at the entrance of the international terminal after police fired at them.
The official, who spoke on condition of anonymity, was citing information from the interior ministry.
It wasn't immediately clear why his account of the number of attackers was different to the justice minister's.
A witness told Reuters one of the attackers "randomly opened fire" in the terminal building before the explosions.
Presidential sources say Turkish President Recep Tayyip Erdogan met with the prime minister and the head of armed forces at the presidential palace after the blast.
The official 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.
Eyewitness Ercan Ceyhan told CNN-Turk that he saw some 30 ambulances enter the airport.
The private DHA news agency said the wounded, among them police officers, were being transferred to Bakirkoy State Hospital.
Attacks on Istabul
Istanbul, a major tourism hub that is home to some 15 million people, has suffered several attacks in recent months, including a bombing in the heart of the tourist district that killed a dozen German visitors and was blamed on IS.
Two months later, three Israelis and an Iranian were killed in a bombing on the city's main Istiklal shopping street, an attack also blamed on IS.
A blast on the tarmac at the other Istanbul airport, Sabiha Gokcen, killed a cleaner and wounded another in December, damaging several planes.
Located just outside Turkey's biggest city, Ataturk airport served more than 60 million passengers in 2015, making it one of the busiest in the world.
Turkey has been hit by at least five attacks blamed on IS jihadists, including a blast in Ankara in October 2015 that left over 100 dead.
However, IS extremists have never formally claimed responsibility for an attack in Turkey.
Turkey was long accused by its Western partners of turning a blind eye to the dangers posed by IS but has in recent months considerably stepped up police raids on the group's cells in the country.
Ankara has meanwhile launched a sustained offensive against the outlawed rebel Kurdistan Workers' Party (PKK) following the collapse of a ceasefire last year.
Hundreds of members of the Turkish security forces have been killed in PKK attacks since the truce collapsed.
More than 40,000 people have been killed since the PKK took up arms in 1984 demanding a homeland for Turkey's biggest minority.
The group is regarded as a terrorist organisation by Ankara and its Western allies.
