It is hard to dispute that Iran's geopolitical importance, both internationally and regionally, has been on the rise over the past decade.

With the Arab Spring, the Islamic Republic saw a new opportunity. For Tehran, the Arab uprisings meant "the awakening of Islam," the rise of Islamist political parties sympathetic to Iran's plight, and a defeat for the Americans, Israel and the West.

But contrary to Tehran's expectations and to the regime's discourse, the Arab Spring does not herald a new ascending phase for Iranian power. Instead, it marks the beginning of a reversal of circumstances.

Tehran, which had initially presented itself as a supporter of the revolutions in Tunisia, Egypt and Libya, was confronted with a dilemma when the Arab Spring reached Syria. Faced with the risk of its only real Arab ally being endangered, it decided to call the protests against Bashar al-Assad's regime a "foreign plot" instigated by Westerners.

Despite a slight hesitation during the summer of 2011 - at least rhetorically - Tehran supported and continues to support the Syrian regime by any means necessary. It has provided political backing and, in terms of security, it has relayed Syrian propaganda and advised the authorities on repression and cyber-warfare against opponents. Tehran has also provided key economic assistance to Damascus.

More recently, it threatened to activate its military alliance with Syria in the event of outside intervention. It finally tried to create a front of pro-Assad states during a recent diplomatic conference that was organized in the Iranian capital at the beginning of August - without great success.

It is true that its position has increased Iranian influence in Damascus in the short term. But it has already started to have negative effects for Tehran. For the past few months, longtime Palestinian allies Hamas have distanced themselves from Iran.

Meanwhile, Hezbollah, the Islamic Republic's Lebanese ally - which also supports the Syrian regime - has seen its public image deteriorate in the Sunni world. Its isolation has increased in Lebanon, where some, even within the Shiite community, are questioning the legitimacy of this support for Damascus and the risks it incurs for all Shiites.

It is clearly going to become increasingly costly for this movement to maintain its proximity with Assad's regime - and a weakening of Hezbollah has repercussions for Tehran. The Tehran-Damascus-Hezbollah and Hamas axis is already weakened.

A sullied image in Arab eyes

That's not all. Because of the situation in Syria, the close relations developed between Tehran and Ankara since the Islamist AKP came to power at the beginning of the last decade have also cooled. Meanwhile, the Syrian crisis further feeds Iran's ongoing rivalry with Saudi Arabia.

But more generally, Iran - like Hezbollah - had built a rather positive image in Arab public opinion because of its anti-Israeli positions, but it is now heavily criticized in the Sunni Arab world for lining up behind the Syrian regime.

In the longer term, if Assad's opponents end up toppling the power in Damascus, the Iranian regime will be in a very delicate position. If ties are cut with a potential new Syrian government, all of Tehran's policies in the region -- and across the Mediterranean -- will be put into question.

This will toll the bell on 30 years of Iranian foreign policy in the region, considerably reducing Tehran's influence in the Middle East. Turkey's position, on the other hand, will be reinforced after its condemnation of the regime's crackdown on rebels.

But whatever happens, Tehran will pay a political price for its unconditional support of Assad.

The downfall of the Syrian regime could also have consequences in Iraq, as the arrival of a Sunni power structure in Damascus could embolden the Iraqi Sunni minority, in a very unstable country where Iran's influence isn't as strong as some imagine.

And finally, the Syrian shock wave could have internal consequences in Iran, by showing that even an extremely violent regime cannot stand in the face of a determined opposition. This could revitalize the Iranian opposition, which was largely quieted after a bloody June 2009 crackdown of post-election protests.

Faced with the fall out of the Arab Spring and weakened by the 2009 events, confronted with an unprecedented crisis of legitimacy and deepening economic difficulties in the face of international sanctions for its nuclear program, the Iranian regime now risks finding itself on the "wrong side of history."

*Mohammad-Reza Djalili is a professor emeritus at the Graduate Institute in Geneva and Thierry Kellner is a political science professor at the Université Libre in Brussels.