Deutsche Welle: Does the suicide bomber attack in Istanbul have terrorist organization "Islamic State" (IS) written all over it?

Günter Meyer: All indicators are pointing in that direction. The first attack took place in June 2015, in Suruc, near the Syrian border. After that, in October, two terrorist attacks in Ankara killed 100 people and injured over 240. The latest attack fits in with the series of attacks – especially since Islamic State has boosted propaganda targeted at Erdogan. In the latest issues of the "Islamic State's" propaganda magazine "Dabiq", Obama and Erdogan have been portrayed as the organization's greatest opponents. With all this in mind, all signs indicate that IS is also responsible for the attack in Istanbul.

Now Turkish police have arrested Russian citizens who are apparently connected to the terrorist group. How can that be interpreted?

When one speaks of arrested Russians, then they are probably jihadists from the Caucasus – most likely Chechnya. Since autumn 2014, the number of IS fighters from this region has risen to over 1,500. Until now, Turkey has tolerated transiting IS supporters and over 2,000 jihadists entering Turkey from the Muslim republics of the former Soviet Union in Central Asia, who have joined IS in Syria and Iraq.

Turkey has often been accused of turning a blind eye to IS in its own country. It is said that Turkey even tolerates it, as foreign fighters have unrestricted entry to Turkey in their travels to Syria. Why is IS fighting Turkey, of all countries?

From the Turkish viewpoint, in the past, IS has supported the two most important goals Erdogan wants to reach in Syria. One goal is to bring down the Assad regime in Damascus and replace it with a pro-Turkish, Sunni regime. The other one is to do anything in his power to prevent the establishment of an autonomous Kurdish region or state along the southern Turkish border to Syria. So the early "Islamic State" military victories against the Kurds in northern Syria and the capture of Kobane were thus in Turkey's interest.

But a turning point has come, especially because Turkey has allowed the US to use the Incirlik air base to launch air strikes against IS. German reconnaissance missions are also launched from Incirlik. That is obviously not in the interest of the terrorist group.

Turkey has thereby become part of the anti-IS coalition, which it also weakens by fighting against the Kurds. How does that work?

In the past, Turkey has not only supported the delivery of weapons and other logistic supplies to IS but it has also permitted free access of foreign IS supporters to Syria. Wounded IS fighters have been treated in Turkish hospitals. Financial support for IS sympathizers from the entire Islamic world has been organized in Turkey. The country has also benefited from the purchase of Syrian oil and thus guaranteed a main source of IS revenue. But we have now clearly reached a turning point: Turkey's support of IS has been dwindling – mainly because of US pressure.

Who will fight IS in Syria – as envisaged by Ankara and Washington – if not the Kurds?

The American side has placed hopes on the democratic forces of Syria, which have joined together to become "Democratic Forces of Syria" – that is he the official name - on October 10, 2015. They consist of about 20,000 Kurdish fighters from the Kurdish People's Defense Units (YPG), 5,000 Sunni Arabs from northern Syria, the tribal militia of the Shammar tribe and an Assyrian-Aramaic Christian militia. They have come together under US leadership and receive military supplies from the US. These forces have made significant territorial gains against IS; just two weeks ago, they took a dam on the Euphrates River and thus severed an important "Islamic State" supply line between Aleppo and Mosul. They have now advanced further towards Aleppo. The Syrian town of Manbij, one of the main centers of IS, risks falling in the near future. So from this viewpoint, the alliance has achieved considerable success with US support.

When IS lost the Syrian town of Tell Abyad, it also lost its most important connection to Turkey. Now, after the sensitive loss, does IS want to demonstrate its presence and power?

That may well play a role. The terrorist organization has suffered a 30 percent loss of its maximum territory size. Thus, losses suffered by IS can be seen as a reason to take action against Turkey and put the Turkish government under even more pressure.

How strong is IS in Turkey?

IS has an abundance of sympathizers. There are estimates of more than 500, some even say up to 1,500 Turkish IS sympathizers, many of which have also joined the battle in Iraq, or in Syria.

Was the attack aimed at weakening the tourism sector or does IS also want to create a power vacuum in Turkey?

A direct attack on Turkey is highly unlikely to happen, but a destabilization of Turkey and related threats are possible. The message is, "If you continue to take action against us, then the attacks will be stepped up." IS has shown that such attacks are quite effective, especially with regard to the economy. The attacks in Tunisia mean that tourism has collapsed for the most part. The economic situation there is deteriorating. The bomb attack on the plane flying over the Sinai Peninsula with Russian tourists on board has led to a massive slump in Egyptian tourism. IS clearly aims to destabilize Turkey economically in order to weaken the government in Ankara.

Professor Günter Meyer is the head of the Center for Research on the Arab World (CERAW) at the University of Mainz in Germany.

DW's Diana Hodali conducted the interview.