Syrian rebels may soon be fighting an enemy assisted by an experienced ally that knows this kind of warfare well: Iran.
Iran's role in Syria's war makes a quick conclusion unlikely
Syria's Bashar Al Assad is still in power, although he is hardly "president" of a country in anything besides name. The opposition forces have shown signs of fracturing and in some areas are losing ground as the regime fights back to regain territory. The international community grows more wary of intervention and is losing faith in both the military capabilities of the opposition fighters and in their true intentions.
Recent developments may have given the regime reasons to be optimistic, despite continued fighting in Aleppo and the assassination of top leaders. Opposition forces have been complicit in a number of atrocities and human-rights abuses, undermining their efforts to obtain further technical, military and financial support from outside Syria.
An array of disparate groups are now fighting the government's troops including, most worryingly, Islamist extremists who are taking control of the uprising. These extremists, who have been known to fly Al Qaeda's flag, also are among the most effective of opposition fighters, and probably will be prominent if and when the regime falls.
Last week, US Defense Secretary Leon Panetta accused Iran of helping to train and assist militia forces inside Syria, to relieve regime army units fighting the rebels. The claim followed reports that several officers of Iran's Revolutionary Guard were among the 48 hostages seized by rebel fighters in Damascus, and a recent claim by a senior Iranian commander that Iranian forces were active in Syria.
This is bad news for the opposition and its international backers, since Iranian military support will probably stiffen the regime's resolve and, at the least, prolong the conflict.
Active Iranian military advisers help the regime in two ways.
First, Iran can teach Syrians what few states know how to do effectively: defeat armed, non-state entities such as the ragtag groups now engaged in urban warfare. Iran knows all about such groups; it has created, trained and armed insurgent groups of this type for more than three decades - and with effect, as US and British forces found out in Iraq after the 2003 invasion. If anyone knows the tactics of such groups, Iran does.
The Syrian regime can also draw some confidence from recent events in Iraq, and Iran's role there. Many Shia militias, battle-hardened from fighting against US and British forces, were under the guidance of Tehran's military commanders. Some of these groups are still intact.
Shia militia leaders have claimed credit for forcing the British out of Basra in 2007, and the US out of Iraq in its entirety in December. Those claims are debatable, but the fact remains that these militias are still in Iraq, while the Americans and the British have gone.
The second role of Iranian-organised and -trained militia forces in Syria will be to have a chilling effect on potential foreign intervention, including a possible no-fly zone or humanitarian safe havens. If western powers believe that Iran is operating in Syria, they will be wary that an intervention could open a Pandora's box for regional stability and the possibility of a proxy conflict.
It is clear that a large-scale intervention now threatens to lead to a protracted war - that would require taking on the diehard elements of the Syrian army, which could be supported by Iranian-trained militias and, possibly, even Iranian forces. The recent hostage-taking of Iranian "pilgrims", who rebels claimed were Revolutionary Guard, indicates a growing likelihood that Iranian advisers will become directly involved.
If the Syrian regime does fall, a proxy war could turn into a protracted civil war, stoked and prolonged by outside forces. The claim by Iran is training a militia army makes a bloody sectarian civil war more probable, somewhat similar to what happened in Iraq between 2006 and 2007 - a conflict in which Iran played a significant part. In the absence of a commitment of western or Nato forces, the better comparison might be with Lebanon's civil war, which lasted more than 15 years and resulted in over 150,000 death.
Syria's opposition fighters, so far, have had a tactical advantage as a loose-knit, dispersed militia force that has stretched the regime's forces and depleted its resources over a year of conflict. However, the rebels may soon be fighting an enemy that is acquiring comparable military advantages, with the help of an experienced ally that knows this kind of warfare well. Iran has a well-organised military model and possesses sophisticated weaponry. It might substantially turn the tide in this civil war.
Ranj Alaaldin is a senior analyst with the Next Century Foundation, a conflict-resolution NGO based in London
On Twitter: @ranjalaaldin