A rebel commander who previously worked for President Bashar Assad’s army along with dozens of people were killed on Monday after a series of Russian air strikes hit the Northwest region of Syria.

Activists reported to ABC News that the attack was one of the deadliest incidents since Russia began their airstrikes three weeks ago. The head of the Britain-based Syrian Observatory for Human Rights, Rami Abdurrahman, stated that at least 45 people were killed, including civilians and rebels. Overall, the group states that Russia’s aerial assaults have killed 370 people, and one third of those are civilian deaths, according to Reuters.

The group of rebels call themselves the “Free Syrian Army” and has received foreign military aid from the U.S., including very powerful anti-tank missiles. The group also confirmed the death of Basil Zamo, its chief of staff.

Russia continues to claim that their air strikes are aimed at defeating ISIS but multiple news agencies, including ABC News, report that many of the areas hit by the air strikes have not been occupied by ISIS, but rebels.

The International Business Times reports that medical organizations in the area are accusing Russia and the al-Assad regime of targeting hospitals in the northern province of Syria. Three hospitals have been hit and two of the hospitals were closed. One was closed due to no longer being operational, and the other closed after medical staff decided to evacuate, fearing they would be targeted further by Russian forces.

The conflict in Syria has resulted in the deaths of more than 250,000 people since the civil war began in March 2011, according to ABC News.