A rebel onslaught on the town of Khan Touman near Aleppo last week delivered one of the biggest battlefield setbacks yet to the coalition of foreign Shi'ite fighters waging war on behalf of Syrian President Bashar al Assad.
Reports put the death toll among the Iranian, Afghani and Lebanese militiamen as high as 80 in the attack spearheaded by the al Qaeda-linked Nusra Front. At least 17 of the dead were Iranians, seemingly the highest toll in a battle outside the Islamic Republic's borders since the Iran-Iraq war.
Events in Khan Touman were followed by an even bigger blow to Iran and its allies: news emerged early Friday of the killing of Hezbollah commander Mustafa Badreddine, who had been overseeing the Lebanese group's military operations in Syria.
It is unclear how such reversals will affect the course of a war that grew out of Arab spring-inspired protests in 2011 calling for democratic change. Before Iran, Hezbollah and Russia came to Assad's aid, his grip on power appeared to be failing. The commitment of these allies to support him is seen by diplomats and Middle East experts as key to Assad's survival.
Such blows are evidence of the price being paid by Iran and Hezbollah in Syria, and the wide range of adversaries they face in a multi-sided war that has escalated again in recent weeks as UN-led diplomacy has foundered.
The Syrian Observatory for Human Rights and a rebel fighting in the area said the intensity of recent Russian air strikes had diminished. That could be a source of friction between the alliance supporting Assad, analysts of the conflict say.
The attack by Nusra and its allies on Khan Touman created shockwaves in Iran. Sites linked to the Iranian Revolutionary Guard Corps published the names and photos of 13 Iranians killed in Khan Touman. Most of them were from a unit of the Guard in Mazandaran province in northern Iran.
But there were concerns among some Iranian officials and military leaders that the report of heavy casualties could sway public opinion against Iran's involvement in Syria.