WASHINGTON (Reuters) - Eleven civilians were killed in four separate air strikes by the U.S.-led coalition fighting Islamic State in Iraq and Syria between Oct. 25 and Dec. 9, the U.S. military said on Thursday.

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

In an incident on Dec. 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 2,358 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 Jan. 31, with 10,993 in Iraq and 6,868 in Syria, according to U.S. military data.

The total cost has been $10.9 billion at an average daily cost of $12.5 million.