The Islamic State (IS) is running out of money and will as a result no longer exist as a territorial state in three years, a German political scientist claims.

Shrinking oil revenues will lead to the end of the group's existence as a territorial state, Professor Harald Mueller from the Goethe University of Frankfurt said in an interview with Austria Press Agency during a visit to Vienna.

Alongside income sources such as taxation, extortion, kidnapping, human and drug trafficking, and spoils of war, oil has been of major importance to the group. On the back of massive air strikes on oil fields, refineries, and transport routes, as well as the major drop in the price of oil, Mueller said this income has in recent times "fallen sharply."

This in turn has led to IS not being able to adequately pay its fighters, or provide necessary financial support for their families. In addition, in some regions both water and electricity shortages are present.

Mueller said this has led to a high number of deserters, because "one can simply not properly live in the IS region."

In contrast to Europe-based jihadists who typically fight for ideological reasons Mueller said the majority of those who fight for IS are from poorer countries, and for whom pay is more important.

It is now a question of whether the numbers leaving the group will turn into an "avalanche," and he believes if this does occur it will accelerate the collapse of the group.

He noted however that IS will not lose its existence as a terror network, and that its loss of capacity as a group could lead it to compensate through more terror attacks including those in western nations.

He said in order to combat the group a continuation of air strikes on IS oil infrastructure that has been led by the U.S. must continue. In addition there must be increased efforts particularly from both Turkey and intelligence services, who must work with police, soldiers, and the financial sector to uncover cross-border financial transactions from the group, such as in the purchase of weapons.

Turkey must also be more vigilant in controlling the smuggling of oil from Syria and Iraq into its territory,he said, noting that while some efforts have already been made, more are needed.