WASHINGTON (Reuters) - The U.S.-led coalition killed 54 civilians between March 31 and Oct. 22 while carrying out air strikes against Islamic State targets in Iraq and Syria, the U.S. military said in a statement on Thursday.

Up to 24 civilians were killed in one strike in mid-July near the Syrian city of Manbij, the statement said.

At the time the opposition Syrian National Coalition called for a suspension of the air campaign against Islamic State in Syria while reports of the Manbij strike were investigated and U.S. Defense Secretary Ash Carter said reports of those civilian casualties would be investigated.

The Britain-based Syrian Observatory for Human Rights had said at least 56 civilians were killed in air strikes north of Manbij.

On July 18, about 100 Islamic State fighters were preparing for a counter attack against Syrian Democratic Forces near Manbij, the statement said.

“Unknown to coalition planners, civilians were moving around within the military staging area, even as other civilians in the nearby village had departed over the previous days,” the statement said.

It throws light on the challenges in coalition air strikes against Islamic State in parts of Iraq and Syria where the United States does not have ground forces or reliable informants within the population.

This brings the total number of civilians killed by the Coalition to 173 since strikes started in 2014, which is significantly lower than estimates from other groups.

In October, Amnesty International said the U.S.-led coalition fighting Islamic State had not taken enough precautions to avoid civilian casualties in Syria and that as many as 300 civilians have been killed in 11 attacks conducted by the coalition since September 2014.

The United States has conducted 12,633 air strikes in Iraq and Syria as of Nov. 17, according to U.S. military data.

The operation against Islamic State in Iraq and Syria has cost $10 billion since 2014.