An explosion in the center of the tourist district in Istanbul killed at least 10 people earlier today, and the Turkish government has already concluded that a Syrian-born suicide bomber carried out the attack. The attack took place at the Sultanahment district, one of the main tourist and historic sites in the city, which encompasses both the Haga Sophia and the Blue Mosque. Officials in Turkey believe the bomber to have ties to ISIS:

A Syrian-born suicide bomber triggered a blast Tuesday in the heart of one of Istanbul’s main tourist districts, a senior official said, killing at least 10 people in a further sign of the country’s deepening instability in a region wracked by war.

The attack struck directly at a hub of Istanbul’s important tourism trade, reflecting similar tactics used by militants against popular sites in countries including Tunisia and Egypt.

Turkey’s deputy prime minister, Numan Kurtulmuş, told reporters that the attacker was identified as a Syrian, but gave no other details following an emergency meeting of security officials.

There was no immediate claim of responsibly, but Turkish officials have blamed the Islamic State for recent bombings elsewhere in Turkey. In addition, Kurdish separatists and domestic left-wing groups have carried out attacks in Turkey.

The Financial Times points out that Turkish officials have an unfortunate wealth of choices for enemies these days. Kurdish separatists in the PKK have conducted also conducted bombings in Turkey. This time, Turkey seems to have settled on ISIS quickly, though:

Almost exactly three months ago, two bombings in Ankara killed nearly a hundred people at a peace rally staged by Kurdish leftists, an unlikely PKK target. This would also be an unlikely target for the neo-Marxist PKK, so perhaps it should not surprise anyone that Turkey has settled on ISIS as the main mover and motivation for this attack. ISIS and its al-Qaeda allies routinely target commercial and tourist areas when plotting attacks, and this attack may produce a major impact on both areas of Turkey’s economy.

As it happens, I have been to the Sultanahmet district when I visited Istanbul in November 2013. We spent a few days there after traveling through the Holy Land. This is the view of the Haga Sophia from the plaza:

This was taken on a cold and gloomy day, but there were still plenty of people in the plaza — perhaps more than this picture actually suggests. One question that might arise would be why the bomber chose to conduct an attack in the plaza rather than in one of the historical sites connected to the plaza. the Haga Sophia, for instance, would have been an obvious choice as a former church and mosque now converted to a museum, but there is also the Blue Mosque and Topkapi Palace connected to the same complex (in this picture, the Blue Mosque is behind me and Topkapi off to the right and down a short path). The answer is probably that the security to enter all of these places is rather significant, which made the plaza a better target of opportunity. That calculation may not hold for long, though, and those priceless buildings are under threat.

The question will be whether this pushes Turkey into a more aggressive position against ISIS. Turkey has wanted to push Bashar al-Assad out by any means necessary, and they gave thousands of jihadis safe transit into Syria to defeat him. They are paying the price for playing footsie with ISIS now, but it remains to be seen whether Erdogan will finally and fully commit to defeating ISIS as the top priority in the region.