BEIRUT - Air strikes by US-led forces have killed 553 people, including 32 civilians, during a month-long campaign in Syria against Islamic State militants, a Syrian monitoring group which tracks the violence said on Thursday.

The Britain-based Syrian Observatory for Human Rights said the majority of the deaths, 464, were Islamic State fighters. Six of the civilians were children and five were women, the Observatory said.

It said 57 members of the al Qaeda-affiliated Nusra Front were also killed in the air strikes, which started a month ago. Strikes hit the provinces of Aleppo, Deir al-Zor, Idlib, Raqqa and al-Hassakah, it said.

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