Rebel groups including the powerful Ahrar al-Sham faction and former Al-Qaeda affiliate Fateh al-Sham Front fired waves of rockets into government-held western Aleppo, killing at least 15 civilians, a monitor said.

The rebels also targeted government positions east of Aleppo city and in the coastal province of Latakia, including the Hmeimim military base that is used by Russian forces allied with the regime.

The assault comes more than three months into a government siege of eastern Aleppo, where over 250,000 people live, and several weeks after the army began an operation to retake the rebel east.

Rebel groups “announce the start of the battle to break the siege of Aleppo,” said Abu Yusef Muhajir, a military commander and spokesman for Ahrar al-Sham.