Russia may be losing its leverage over Assad and Iran in Syria

A cease-fire agreement aimed at stopping the battle for Syria's largest city long enough to evacuate civilians and rebel fighters has already collapsed, less than one full day after it was brokered in Ankara by Russian and Turkish officials.

It is unclear who broke the truce first. Moscow, which backs Syrian President Bashar al-Assad, accused the rebels of rupturing the fragile peace, while the opposition said pro-Assad Shiite militias resumed their attacks on besieged districts of eastern Aleppo early Wednesday morning.

The militias, which are backed by Iran, halted the evacuation of the first group of civilians, a source within the opposition told Business Insider on Wednesday. The source said the militias demanded injured Shiites in the villages of Foua and Kafraya in the rebel-held Idlib province - where the rebels and civilians were to be sent - be evacuated first.

The source said Iran had expressed fears that the Shiites would face retribution if Sunni Arab rebels were allowed to leave eastern Aleppo. But Osama Abo Zaid, a legal adviser to Aleppo's rebel groups, said Iran was being motivated by "exclusively sectarian and crippling" considerations.

Iran, a staunch ally of Assad that arms and funds the Shiite militias fighting on his behalf, reportedly felt blindsided by the terms of the truce brokered in Turkey between Russia and the rebels.

"Iran considers the Russian deal with opposition, facilitated by Turkey, a deal made without their knowledge and intended to sideline Iran," Syrian journalist Hadi Alabdallah tweeted Wednesday. "For this reason, Iran-backed militias [have] obstructed the evacuation of the injured since yesterday until now, highlighting Russia-Iran discord over Syria."

Noah Bonsey, a senior analyst in the Middle East and North Africa program at the International Crisis Group, said that "if reports now are accurate, it seems Russia lacks the leverage to implement evacuation deal in Aleppo, and Iran is unwilling. Speaks volumes."

Further complicating the negotiations is the feeling that Russia, which turned the tide of the war when it launched an air campaign on behalf of Assad in October 2015, is quickly losing influence over Iran and the Assad regime itself - especially given the regime forces' broadly successful ground invasion of eastern Aleppo over the last month.

Russia has been trying to convince the Assad regime to accept the conditions of the truce, a spokesman for the Aleppo-based rebel group Noureddine Zinki told The Guardian on Wednesday. But Iran, whose proxy militias wield considerable power on the ground in Aleppo, was unwilling to accept the terms of the deal, said Asaad Hanna, a political officer in the opposition Free Syrian Army.

"The Iranians have so far refused to accept the outcome of the talks, even as Russia accepted many requests made by the opposition," Hanna told Business Insider on Wednesday.

"Because the Russians don't have fighters in Aleppo, like the Iranians do through their proxies, they cannot apply the cease-fire deal on the ground, in practice," he added. "They have to deal with the Iranians because its their militias who are controlling the checkpoints and largely directing the pro-Assad forces in Aleppo."

The opposition is still negotiating with the Russians in Ankara, Hanna said, but will not meet with the Iranians directly. Iranian Foreign Minister Javad Zarif will meet with his Turkish and Russian counterparts in Ankara on Wednesday, however, to discuss the terms of the truce, according to Reuters.

Russia and Iran, both staunch allies of Assad, have broadly been on the same page in Syria throughout the course of the war. Russia reportedly intervened in the conflict at the request of Iranian Gen. Qassem Soleimani, who visited Putin in August 2015 to request Russia's help in bolstering Assad.

The newly fortified Russian-Iranian military alliance gave Putin more leverage and influence in the region in the short-term, and was therefore as beneficial to Moscow as it was to Tehran.

Now that Assad has essentially won his biggest victory of the five-plus year civil war, however, and is in control of Syria's major urban areas, he and his Iranian allies may not feel as indebted to - or dependent on - Russian airpower.

Still, Cliff Kupchan, an expert on Russia and Iran at the political risk firm Eurasia Group, said that current tension between Russia and Iran should not be overstated, and that it is likely as much the Russians' as the Iranians' fault that the evacuation deal has not been implemented.

"The deal will be implemented at some point," Kupchan said. "But before they follow through on it, the Russians and Iranians are trying to maximize their leverage and concessions from the armed rebels. They're trying to see the rebels leave in as few numbers, and with the least amount of weapons, possible."

Indeed, Turkey's foreign minister, Mevlut Cavusoglu, told reporters on Wednesday from Ankara that "Russia, Iran, forces supported by Iran, and the regime" were "trying to obstruct" the deal.

The US has been shut out of the Ankara talks, but the State Department said Wednesday it was aware of reports that implementation of the cease-fire and evacuation plan had failed "due to intense shelling on civilian neighborhoods in east Aleppo."

"We urge all parties involved to get a cessation of hostilities back on track, permit departures for all those who want to leave the city, and allow deliveries of humanitarian assistance to all in need," a State Department official told Business Insider on Wednesday.

"We strongly urge Russia, the Syrian regime, and Iran allow for UN monitoring as a safeguard against further atrocities," the official said. "The world is watching."