Eleven killed in Iraqi, Syrian air strikes

Eleven civilians were killed in four separate air strikes by the US-led coalition fighting Islamic State in Iraq and Syria between October 25 and December 9, the US military said on Thursday.

"Although the Coalition takes extraordinary efforts to strike military targets in a manner that minimises the risk to civilian casualties, in some incidents casualties are unavoidable," the military said in a statement.

In an incident on December 7, near Raqqa, Syria, the military said seven civilians were killed in an air strike on a building where Islamic State fighters were present.

The number of civilians killed since the start of the air campaign in 2014 totals 199, the statement added, but the estimate is far lower than those provided by monitoring groups.

At least 2358 civilians have been killed by coalition air strikes, according to monitoring group Airwars.

The coalition has conducted more than 17,861 air strikes since the start of the operation, as of January 31, with 10,993 in Iraq and 6868 in Syria, according to US military data.

The total cost has been $US10.9 billion ($A14.2 billion) at an average daily cost of $US12.5 million.