The monitoring group said that the dead included both prisoners and prison guards, adding that it had received information that a number of prisoners were shot dead while attempting to flee after airstrikes struck the prison.
Syrian regime and Russian aircraft routinely conduct aerial missions over Idlib province, which is a key stronghold of rebels, including extremist factions fighting against forces loyal to Syrian President Bashar al-Assad.
The US-lead coalition has also carried out airstrikes in Idlib province targeting Islamic State group militants. Earlier this month it said it was investigating claims that over 40 people were killed in airstrikes it carried out in the province, which borders Turkey.
Idlib city was the second city in Syria to fall from government control in March 2015 when it was captured by a coalition of rebel groups called the Army of Conquest which included the al-Qaeda affiliated al-Nusra Front, now rebranded Fateh al-Sham.
Despite a ceasefire deal brokered by Turkey, which backs rebels fighting against Assad, and regime ally Russia, violence continues unabated on many fronts across Syria.
The Syrian conflict began when the Baath regime, in power since 1963 and led by President Bashar al-Assad, responded with military force to peaceful protests demanding democratic reforms during the Arab Spring wave of uprisings, triggering an armed rebellion fuelled by mass defections from the Syrian army.
According to independent monitors, hundreds of thousands of civilians have been killed in the war, mostly by the regime and its powerful allies, and millions have been displaced both inside and outside of Syria. The brutal tactics pursued mainly by the regime, which have included the use of chemical weapons, sieges, mass executions and torture against civilians have led to war crimes investigations.
