The rebels' capture of Kindi hospital does not drastically alter the broader battle for Aleppo, which has been divided for more than a year between opposition and government forces.
But it does provide a lift to a rebel movement that has been dogged in recent months by infighting that allowed President Bashar Assad's forces to chip away at rebel-held territory on several fronts.
For months, rebels had been trying to capture Kindi hospital, which is close to the besieged central prison on the edge of town and where the government is believed to be holding thousands of detainees.
Aleppo-based activist Abu al-Hassan Marea said the rebels who overran the hospital included both conservative Muslim groups and al-Qaida-linked factions.
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At least 35 rebels were killed in the battle for Kindi, the activists said. There was no immediate death toll available for government forces.
A Syrian freelance photographer who worked for foreign news outlets, including Reuters, also was killed in the fighting, activists said. The photographer, Molhem Barakat, was with his brother, a rebel fighter, inside a carpet factory near the hospital when they were both killed, said Hassoun Abu Faisal of the Aleppo Media Center. Activists also circulated a photograph of Barakat's corpse, which matched other images of him.
Media watchdog groups have ranked Syria the world's most dangerous country for reporters. The Committee to Project Journalists says 22 journalists have been killed in Syria this year, not counting Barakat. More than 30 journalists are believed to be currently held by the Syrian government or rebel forces.
Meanwhile, Syrian government forces continued dumping so-called barrel bombs, containers containing hundreds of kilograms of explosives and fuel, over opposition-held parts of Aleppo.