To the northeast, a Western-backed alliance of Arab and Kurdish fighters scored a major victory against the Islamic State group in the town of Manbij after a fierce two-month battle.
The developments have rocked the key northern province of Aleppo, a microcosm of Syria's topsy-turvy, multi-front war that has killed more than 280,000 people.
Rebel and regime forces have fought for control of the provincial capital of the same name since mid-2012, transforming the former economic powerhouse into a divided, bombed-out city.
"The Army of Conquest... Took control of the armament school, where there is a large amount of ammunitions, and a large part of the artillery school" at a military academy, said the Syrian Observatory for Human Rights.
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The coalition of rebels, Islamists, and jihadists "is about to cut off, by gunfire, the supply route into government-controlled districts," said Observatory head Rami Abdel Rahman.
That road passes through a southwestern suburb of Ramussa and is the last route into Aleppo used by regime troops.
"Days ago, I was only thinking about how to get a bite to eat," said Ahmad Adna, a 46-year-old resident of eastern Aleppo.
"Now I'm more optimistic after the Army of Conquest's advance. I hope today will be the last day of the siege."
The former Al-Nusra Front - renamed Jabhat Fateh al-Sham after breaking from Al-Qaeda - today announced having captured the two military academies and a third military position.
Drone footage posted by the group online showed a series of explosions in some of those buildings, followed by massive columns of billowing black smoke.
Abdel Rahman said the advance left the regime forces "in a very difficult position despite Russian air support."
"This is an existential battle. Whoever wins it will win Aleppo."
State media reported fighting in the three locations and said the army had dispatched reinforcements in a counter- offensive to take on "thousands of terrorist fighters".
An army officer told state television troops had advanced in the areas seized by rebels and was inflicting "heavy losses" on them.