A Syrian monitor says at least 16 people have died in airstrikes on a prison in northwestern Syria.

The Britain-based Syrian Observatory for Human Rights on Saturday said prisoners and staff were killed in the strikes in the rebel-held city of Idlib.

The Observatory says it has received reports that some of those killed were fleeing after the airstrikes and were shot by prison staff members.

Idlib is an opposition stronghold where Russian warplanes have been known to carry out strikes in support of Syrian President Bashar al-Assad.

Since 2011, the conflict in Syria has killed 400,000 people, wounded more than 1 million and displaced half the country’s population.