Rebel factions, backed by the former al-Qaeda affiliate in Syria, have reportedly launched a major offensive to break the siege east of Syria’s Aleppo city by forces loyal to the Russian- and Iranian-backed Syrian Dictator Bashar al-Assad.

Jabhat Fateh al-Sham (JFS), formerly known as the Syrian al-Qaeda offshoot Jabhat al Nusra, is one of the main rebel factions spearheading the operation, reports BBC. Various analysts have dismissed JFS’s break with al-Qaeda earlier this year as a feint.

Since around mid-2012, the provincial capital of Aleppo, once considered Syria’s largest city, has been roughly divided between Assad regime control in the west and rebel control in the east. Aleppo city is the capital of a province of the same name.

“About 275,000 people have been besieged in the east by pro-government forces for several months,” notes BBC.

Syrian rebels from inside and outside Aleppo city have joined the offensive, which marks the second attempt to break the siege.

“All the revolutionary factions, without exception, are participating in the battle,” declared the military spokesman for the Fastaqim faction inside the city, the Associate Press (AP) reports.

Besides JFS, the rebels include fellow jihadists from Ahrar al-Sham.

JFS, which the United States considers an enemy, is one of the major rebel groups leading the offensive, notes BBC, adding, “This means that from a Western perspective at least, the rebels are on their own.”

The operation comes as Russia and Iran have vowed to increase their support for Assad, also reports BBC.

Both sides — the rebels and Assad-allied groups — have recently been accused of killing children amid mutual bombardment.

The Syrian Observatory for Human Rights, a U.K.-based group that uses a network of sources on the ground to monitor the ongoing war in Syria, reported Friday that missiles fired by the rebels into western Aleppo city killed 15 civilians and wounded 100 others, adding that the fatalities are likely to rise given the seriousness of the injuries.

The Observatory noted that the rebels backed by JFS launched at least “150 missiles” into areas southwest of Aleppo city.

At least six children were killed by the missiles fired into Assad-controlled western Aleppo.

JFS-allied rebels also targeted the al-Neirab Assad military airport “with dozens of missiles” wounding “a number of civilians,” adds the monitor group, without specifying how many people were injured.

However, BBC, citing the Observatory, reports that up to 115 people were killed or wounded in the attack on the military airport.

Moreover, JFS-backed rebels carried out three suicide car attacks in southwest Aleppo.

One of the automobiles was driven by a French suicide bomber from JFS, reportedly revealed a spokesman for the group.

On Wednesday, the Observatory noted that Assad shelled several neighborhoods in Aleppo city, troops killing a child and wounding others. The monitor group did not explicitly say how many people were injured.

Meanwhile, deadly clashes continue in the northern countryside of the besieged city of Aleppo between the U.S.-backed Syrian Democratic Forces (SDF), led by the Kurdish People’s Protection Units (YPG), and Turkish-backed Syrian rebels.

Turkey considers the YPG, the armed wing of the Democratic Union Party (PYD), to be the Syrian affiliate of the Kurdistan Worker’s Party (PKK), a communist-separatist group that has been deemed a terrorist organization by NATO allies the United States and Turkey.

However, the administration of President Barack Obama has long argued that the YPG fighters and the PYD are not terrorist groups.

Turkey is in favor of removing Assad from power.

Although the JFS-rebels are constantly fighting against the Assad regime, both sides have a common enemy — the Islamic State (ISIS/ISIL).

The same applies to the U.S.-backed SDF troops and their rival, the Turkish-allied rebels. While all the different factions in Syria, including the Assad forces, are fighting one another, they all consider ISIS to be their enemy.

Nevertheless, Syria and its ally Russia have recently intensified airstrikes on rebel-controlled east Aleppo. Russia has declared that it is time for all rebel groups in eastern Aleppo to be considered “legitimate targets,” reports BBC.

As they confront Iranian and Russian-backed Assad troops and militiamen, including the Lebanon-based Shiite terror group Hezbollah, Iran’s proxy,  the JFS-backed rebels have acknowledged that “liberating” east Aleppo will not be easy.

“The Syrian army is the least of their problems — by itself, it is relatively weak,” points out BBC. “The Syrian government is supported by Lebanese, Iranian, Iraqi and Afghan Shia militias, as well as Russian air power – soon to be bolstered by a naval fleet in the Mediterranean.”