More than 1,300 people, around two-thirds of them combatants, have been killed in Russian air strikes in Syria since Moscow's aerial campaign began on September 30, a monitor said Friday.

The figure supplied by the Syrian Observatory for Human Rights is more that double the overall toll it gave in its last report on the Russian campaign three weeks ago, AFP reports.

The Britain-based Observatory said it had documented 1,331 deaths in Russian air strikes, most of them of ISIS jihadists or other fighters.

It said 381 ISIS fighters had been killed, along with 547 militants from Al-Qaeda affiliate Al-Nusra Front and other rebel forces.

The strikes also killed 403 civilians, including 97 children, according to the monitor.