The US-led coalition bombing the Islamic State (IS) militants in Syria and Iraq said Thursday that 54 civilians had been "inadvertently killed" in seven air strikes between March and October.

"Although the coalition makes extraordinary efforts to strike military targets in a manner that minimizes the risk of civilian casualties, in some cases casualties are unavoidable," the coalition said in a statement.

A July 18 strike that killed 100 IS militants also killed as many as 24 civilians, the statement added.