Deutsche Welle: Washington and London seem to be certain that the crashed Russian airplane was carrying a bomb, meaning that the "Islamic State" carried out a terrorist attack. How can one explain the caution with which the Russians have been commenting on the crash?

Michael Lüders: At such an early point in time, I think one should generally be cautious about accusations. It is still not clear who is behind this crash. Every side that comments has its own interests.

Egyptians do not want to create the impression that the Sinai Peninsula has a terrorist problem in the form of Islamic State. That would mean that tourism in the region would collapse completely. Of course the Russians do not want to worry their population. They do not want to create the impression that a Russian aircraft was actually shot down by a missile fired by Islamic State.

Right now, there are hints that a bomb was in the airplane – that is what the Americans and British say. No evidence has yet been found but of course, it cannot be ruled out that a bomb was smuggled on board the airplane in Sharm el-Sheikh. Safety regulations in Egyptian airports are fairly lax compared to European airports.

That begs the question as to whether the Russians have overextended themselves with their military involvement in Syria.

The Russians are pursuing their own power politics in Syria. They would like the Bashar-al-Assad regime to remain in power, as Syria – like Iran – is Russia's only ally left in the Arab world. Both countries, like China, do not want Syria to fall into the hands of the West or to be completely conquered by the Islamic State.

However one perceives Russian involvement – must we not be frightened that the IS has dared to attack a major world power?

From the IS standpoint, there is nothing more desirable than military invention by foreign forces in Syria or Iraq, if possible with the deployment of ground troops. Of course all IS leaders pulling the strings - mostly former generals of the Saddam Hussein regime – know that foreign forces cannot win battles with guerilla warfare tactics against Syria, Iran or Iraq. By intervening and sending ground troops, a western country, or Russia, would be doing exactly what the IS is waiting for.

Is the common enemy "Islamic State" enough to bring Americans, Russians and Europeans together to form an alliance?

In principle, yes. The Americans have initiated dialogue with Russia and are trying to coordinate their military attacks against Islamic State. But there are still fundamental differences between the Western states that want to bring down the Assad regime and the Russians and Chinese, who want to prevent that from happening.

Up until now, the reasoning of the West was to fight the IS and to bring about the fall of the regime. This idea has proven to be unrealistic. It cannot be carried out by the military.

Bashar al-Assad's regime is on the decline and cannot survive without the help of Russia and Iran, however, there are there are many Syrians – and we like to overlook this fact – who prefer the "plague" known as the Assad regime over the "cholera" of the IS marching into Damascus. That is exactly what would happen if Assad's regime fell apart. It is not as though freedom, democracy, human rights and a moderate regime would come into power, as many advocates of western military intervention would assume.

Michael Lüders holds a PhD in Islamic studies and political science. He is a journalist, political adviser and deputy chairman of the German Orient-Foundation and president of the German-Arab Association.