BEIRUT - The Turkish authorities have accused the Islamic State group of carrying out the attack on Istanbul's international airport that killed 41 people.
Long accused of complacency towards IS, Turkey has changed its approach since joining the US-led coalition against the jihadists in August 2015.
IS has long relied on Turkey as a conduit for reinforcements and weapons bound for Syria to fight the regime of Bashar al-Assad, his armed opponents and Al-Nusra Front, the branch of Al-Qaeda in the war-torn country.
Turkish President Recep Tayyip Erdogan, a devout Sunni Muslim, openly advocated the downfall of his old ally, his Syrian counterpart Bashar al-Assad of the Alawite offshoot of Shiite Islam.
- Earlier report: Casualty toll rises
He therefore supported all components of the rebellion since the start of the conflict in Syria in 2011 that has now killed more than 280,000 people and forced millions to flee their homes.
In August 2015, Turkey joined the international military coalition against IS which, along with Russia, is mainly targeting the jihadists' oil facilities, including many fields and wells.
"Strangely, IS accuses Turkey of lending support to the YPG (Kurdish People's Protection Units) and has blamed Turkey -- and others -- for the loss of territory along the border," says Aron Stein of the Atlantic Council think-tank.
For its part, after having condoned IS's activities, police have been "hitting IS in Turkey pretty hard" including raids in Gaziantep and elsewhere. And Ankara announced recently that its forces were shelling IS positions in Syria.
Although no-one has claimed responsibility for the attack on Istanbul's Ataturk Airport, Prime Minister Binali Yildirim said "the evidence points to Daesh", using another name for IS.
At the height of the attacks, a passenger captured a photo of the carnage after a suicide bomber blew himself up. (Source: Twitter/@IraqiSecurity)
According to the Soufan Group intelligence consultancy, "Turkey has become a prime target for the Islamic State in the last year. It has been mentioned several times in the group's English-language magazine, Dabiq; President Erdogan was featured on the cover of issue 11."
Turkey also believes that IS hit it where it hurts, especially tourism, which brings the country's economy around $30 billion a year.
Ege Seckin of IHS Country Risk says that "the attack was most likely conducted by the Islamic State to undermine the Turkish economy by attacking the airport ahead of the summer months, when tourism peaks."
IS, which is normally quick to claim responsibility and reveal gory details of its attacks, has always been discreet when it comes to Turkey.
Unlike Kurdish separatists, it has never endorsed attacks in the country except against Syrian citizen journalists.
"It's unclear why IS doesn't claim credit, but it appears to be part of a broader strategy to exacerbate internal Turkish tensions, ranging from political polarisation to the Kurdish-Turkish conflict," says Stein of the Atlantic Council.
The airport attack could mark a turning point.
"If the Islamic State is indeed behind this attack, this would be a declaration of war," says Soner Cagaptay, director of the Turkish Research Programme at The Washington Institute.
"Thus far, Turkey has avoided engaging the Islamic State in full war, instead prioritising its battle against the Assad regime and the Syrian Kurds. For Turkey, fighting the Islamic State as a first order battle could now be unavoidable."
Target for bombers
ISTANBUL - Turkey is battling threats on two main fronts - against Islamic State group jihadists and Kurdish militants.
Following is a list of the worst bomb attacks in Turkey in only the past year, compiled by AFP:
June 28: At least 41 people are killed, including foreigners, and over 200 injured in a triple suicide bombing and gun attack at Istanbul's Ataturk airport. There is no claim of responsibility but authorities say evidence points to the Islamic State group.
June 7: At least seven police officers and four civilians die when a bomb rips through a police vehicle near the historic centre of Istanbul. The Kurdistan Freedom Falcons (TAK), a radical offshoot of the rebel Kurdistan Workers' Party (PKK), claims the attack and warns tourists to stay away.
March 19: Three Israelis and an Iranian are killed and dozens injured in a suicide bombing targeting Istanbul shopping thoroughfare Istiklal Caddesi. Pro-government media blame Islamic State extremists.
March 13: At least 34 people are killed and dozens wounded in a suicide car bomb attack in Ankara. The TAK claims the assault.
February 17: At least 29 are killed in a car bombing targeting the Turkish military in Ankara. The attack is also claimed by TAK.
January 12: Eleven German tourists are killed and another 16 people wounded in a suicide attack by a Syrian bomber in Istanbul's Sultanahmet district, the ancient tourist heart of the city and home of the Blue Mosque. Then prime minister Ahmet Davutoglu said the bomber belonged to IS.
October 10: In the bloodiest attack in Turkey's history, 103 people are killed and more than 500 wounded in twin suicide bombings targeting a pro-Kurdish peace rally in Ankara. The prime minister says IS was the main suspect.
July 20: 34 people are killed and about 100 wounded in a suicide bombing in the predominantly Kurdish town of Suruc near the border with Syria. Turkish officials again blame IS.
By Wednesday evening, the airport was back in partial operation, under heavy guard. (Reuters photo)