Opposition members attack Syrian government targets in the Dahiyat al-Assad region located in western Aleppo on Oct. 28, 2016, Aleppo, Syria. Getty Images

Syrian rebels launched Friday a major offensive aiming to break the Syrian government's siege of the rebel-held city of Aleppo, BBC News reported. Rebel forces issued a call-to-arms spanning the entire Syrian opposition to the Assad regime in hopes of breaking a months-long siege that the Syrian army has imposed on the city in an effort to force rebels to surrender.

Jabhat Fatah Al Sham, formerly known as Al Qaeda's Al Nusra Front, was one of the leading forces in the operation. Syrian state-run media claimed militants of the Islamic State group also staged a coordinated attack on the Air Force Academy in southeastern Aleppo. While most participating groups were fighting from outside the city, certain factions such as Fastaqim Union were expected to conduct operations from within Aleppo.

"Preparation has begun for heavy artillery fire on the positions of Assad's gangs in Western Aleppo," the group said in a Twitter post.

Rebels shelled Syrian army positions from all sides of the city. Multiple suicide bombs targeted the southwest. One French Fatah Al Sham fighter reportedly drove an explosion-rigged tank toward government positions and detonated it after fleeing. UK-based monitoring group Syrian Observatory for Human Rights has said at least 15 civilians were killed by rebel-fired rockets and an additional 100 wounded.

While the assault reportedly concentrated on the city's western suburbs, rebels also targeted the Russian-controlled Hmeimim air base in the coastal province of Latakia, about a two-hour drive away. The Syrian army claimed it repelled all rebel attacks without losing any territory.

Iran's Foreign Minister Mohammad Javad Zarif, Russia's Foreign Minister Sergei Lavrov, and Syria's Foreign Minister Walid Moallem (L-R) at a press conference following a trilateral meeting on Oct. 28, 2016. Getty Images

Russia and the Syrian government had intensified their campaign of airstrikes against the city in recent weeks before announcing a humanitarian ceasefire in Aleppo on Oct. 18. They offered a truce that would allegedly allow "moderate" opposition fighters to leave the city, a proposition that opposition forces rejected. Local activists and rebel fighters claimed several airstrikes have been conducted in spite of the pause. Syrian Foreign Minister Walid al-Moallem said Friday at a trilateral press conference with his Russian and Iranian counterparts that rebels had disrupted the ceasefire by targeting those who tried to flee the city. He then stated that the government and Russia were willing to reinstate a cessation of hostilities if rebel forces guaranteed the safety of civilians and those wishing to leave Aleppo through so-called exit corridors.

Prior to the war, Aleppo was Syria's largest city and commercial capital. Since then it has become a flashpoint for the five-year conflict in which the Syrian government and rebel forces have been embroiled. The city has been a stronghold for opposition forces, but the Syrian government encircled it in September and imposed a siege on its Eastern quarters. The United Nations and the West have accused Russia and the Syrian government of inflicting massive civilian casualties, something both entities deny. It is estimated that at least 250,000 civilians remain trapped within the rebel-held areas of the city.