(CNN) After months of being pummeled from the air and by Syrian artillery, an Islamist-led rebel coalition has made a dramatic breakthrough in relieving the siege of Aleppo, Syria's largest city. Their assault -- the first test for a new group born out of al Qaeda's Syrian affiliate -- appears to have taken the exhausted Syrian army by surprise.
If consolidated, the rebels' offensive -- which they have dubbed "The Great Battle for Aleppo" -- could change the landscape of the conflict in northern Syria. What is beyond dispute is that the renewed fighting, and the waves of regime airstrikes and rocket attacks launched in response, is inflicting yet further suffering and destruction in Syria's oldest city.
The rebel offensive has been led by Jabhat Fateh al Sham, formerly the al Nusra Front. Two weeks ago, al Nusra very publicly declared it was breaking its long-standing ties with al Qaeda to build closer alliances with other jihadist and rebel groups in Syria.
"Unifying our efforts and ranks is imperative to meet the goals of the Syrian revolution," Jabhat Fateh al Sham announced, anticipating "a complete merger between all sincere groups."
Its leader, Abu Muhammad al-Julani (who had led al Nusra) spoke of the progress of the Aleppo assault in an audio message on Friday, celebrating "the coalescence and unity of the factions against the enemy."
According to the group's own statements, its suicide bombers have played a key role in the advance, which has included the seizure of a government military complex in the Ramouseh district. State media in Syria have denied the complex was lost, but photographs and video from the area appear to show it in rebel hands.
Drone footage released Sunday by the rebel coalition, which operates under the banner Jaysh al Fateh, shows a rebel tank firing at government positions inside the military complex.
It's unclear how much weaponry may have been seized in the process. Karam al Masri, a freelance journalist in eastern Aleppo, told CNN the rebel coalition was able to gain all the weaponry stored in the complex.
The rebel offensive moved the battle into dense urban terrain, where airpower is less of an advantage to the regime than in the countryside north of the city. According to the Syrian Observatory for Human Rights and other sources in Aleppo, rebel fighters inside the city pushed toward their allies coming from the southwest, eventually linking up on Saturday. Rebel factions posted videos purportedly showing their fighters embracing as they met. Videos were also posted appearing to show dozens of tires on fire to hinder the regime's targeting from the air.
Although the rebel alliance is dominated by jihadist groups, the Aleppo offensive also includes several groups that have been supported by the West, such as Harakat Nour al-Din al-Zenki. That may complicate any discussions between the United States and Russia on how to target jihadist factions in Syria while leaving more moderate groups intact.
Additionally, to many analysts, the rebels' success is a potent message to Syrians who oppose Assad but have felt betrayed by a lack of help from the West. Kyle Orton of the Henry Jackson Society tweeted: "The world abandoned Aleppo; the jihadis came to the rescue. Al-Qaida's rebranding could hardly have asked for more."
Journalist Masri in eastern Aleppo reinforced the point, telling CNN the popularity of the rebel coalition has increased.
In a Skype interview, Masri said the rebel alliance had "promised to help when the siege was enforced. People thought it was just an expression of empathy but when it was backed by actions, their popularity has risen."
"People are impressed that in spite of all the airstrikes by the regime and the Russians, they managed to take territory and break the siege," Masri said.
They are likely to be more impressed if the rebels can begin to bring in much needed basic supplies.
Masri said seven military vehicles brought in goods on Sunday, but the road into eastern Aleppo is full of mines. If they can be cleared and the route secured, more produce can be brought in.
"People are preparing to open their shops and to load their stands," Masri said.
In May, President Bashar al Assad likened the fight for Aleppo to the battle of Stalingrad. In terms of destruction at least, he may have been right.
His regime, with help from Iranian and Lebanese Hezbollah militia as well as Russian airpower, gradually sealed off rebel-held eastern Aleppo in the spring. An estimated 250,000 civilians -- a third of them children, according to the UN Children's Fund -- were essentially locked into a giant open prison. The last road for supplies into eastern Aleppo was cut off in mid-July.
The regime used similar tactics to stifle and eventually snuff out rebels in Homs last year.
Analysts say part of the regime's calculation was that victory or something close to it in Aleppo would strengthen its hand if and when negotiations resumed.
In the meantime, civilian casualties mounted. According to the Institute for the Study of War, "Russian and regime airstrikes during [April to July] increasingly targeted critical civilian infrastructure in opposition-held neighborhoods. The onslaught of airstrikes likely sought to drive refugee flows and prime the civilian population for eventual surrender."
The group Physicians for Human Rights said hospitals have been among the targets, with six struck in the last week of July alone.
On Thursday, regime planes dropped leaflets on eastern Aleppo urging fighters to surrender and civilians to leave.
In retaliation, rebel groups have shelled government-held parts of Aleppo in recent days. Part of their strategy may be to answer the regime's siege with one of their own.
For the rebels, and especially jihadist groups, keeping the uprising in Aleppo alive is critical. Besides the town of Idlib, it is the last major urban area they control -- and a weather vane for the larger conflict.
It's too early to know whether the rebel alliance can sustain its gains, or whether it will be more cohesive in the wake of al Nusra's rebranding outside the al Qaeda franchise. But the rebels' progress -- under the joint banner of Jaysh al Fateh -- is the regime's first serious setback in Aleppo province in months.
Russian airstrikes and Iranian/Hezbollah help on the ground had shifted momentum elsewhere in Syria in favor of the beleaguered Assad regime, which retook the city of Palmyra from ISIS and secured corridors between the capital, Damascus, and other government-held areas.
But beyond the Presidential Palace in Damascus there is nowhere more important to any of Syria's factions than Aleppo. The city's ruin may be completed as the bitterly polarized struggle in Syria moves to its next phase.
And therein lies a historical irony. One of the world's longest continuously inhabited cities, Aleppo was a trading hub 500 years ago, a home to polyglots and a multitude of ethnic and religious groups. When the Englishman John Eldred arrived in 1586, he "was struck by the hustle and bustle created by Jews, Tatars, Persians, Armenians, Egyptians, Indians and many Christians," according to Philip Mansel's new book "Aleppo: The Rise and Fall of Syria's Great Merchant City."
Mansel also quotes an Aleppo proverb of the time: "Excess is obnoxious, even in religious worship." It was a place of co-existence and tolerance five centuries ago.
Now the battle for what remains of the historic city is cast as one between those the regime decries as "terrorists" and those described by Joulani this week as "the Russian dominion and Rafidhi [Shia] malice."
ISIS, meanwhile, which is not involved in the current fighting around Aleppo, will look on with glee at the remorseless battle of attrition among its enemies.