At least 352 civilians have been killed in US-led strikes against Isis targets in Iraq and Syria since operations began in 2014, the Pentagon has said.

The Combined Joint Task Force, in its monthly assessment of civilian casualties from the US coalition's operations against the jihadi group, said it was still assessing 42 reports of civilian deaths.

It added that 45 civilians were killed between November 2016 and March 2017. It reported 80 civilian deaths from August 2014 to the present that had not previously been announced. The report included 26 deaths from three separate strikes in March.

The military's official tally is far below those of other outside groups. Monitoring group Airwars said more than 3,000 civilians have been killed by coalition air strikes.

Included in Sunday's tally were 14 civilians killed by a strike in March that set off a secondary explosion, as well as 10 civilians who were killed in a strike on Isis headquarters in the same month.

“We regret the unintentional loss of civilian lives ... and express our deepest sympathies to the families and others affected by these strikes,” the Pentagon said in a statement.

The report did not include findings from an ongoing investigation into a 17 March strike targeting Isis fighters in the Iraqi city of Mosul. That strike resulted in more than 100 civilian deaths, according to reports from residents. Last month, the U.S. acknowledged coalition planes conducted a strike “at the location corresponding to allegations of civilian casualties,” but did not confirm the reports of high civilian casualties.

Coalition officials have declined to give a time frame as to when the investigation into the incident will be complete.

In pictures: Isis' weapons factories Show all 11 1 /11 In pictures: Isis' weapons factories In pictures: Isis' weapons factories A mortar round fin manufactured by Isis in Gogjali, Mosul, November 2016 Conflict Armament Research In pictures: Isis' weapons factories Isis rocket components discovered in Gogjali, Mosul, Iraq in November 2016 Conflict Armament Research In pictures: Isis' weapons factories Isis mortars discovered near Karamlais, Iraq, in November 2016 CAR In pictures: Isis' weapons factories An Isis rocket launch frame in Qaraqosh, November 2016 Conflict Armament Research In pictures: Isis' weapons factories A memo from Isis' COSQC on quality control at a manufacturing facility in Gogjali, Mosul, November 2016 Conflict Armament Research In pictures: Isis' weapons factories Electrically-operated initiators manufactured by Isis in forces Gogjali, Mosul, November 2016 Conflict Armament Research In pictures: Isis' weapons factories Isis mortar tubes at a manufacturing facility in Karamlais, November 2016 Conflict Armament Research In pictures: Isis' weapons factories An Isis mortar production facility discovered in Gogjali, Mosul, in November 2016 Conflict Armament Research In pictures: Isis' weapons factories An Isis weapons manufacturing facilities near Mosul in November 2016 Conflict Armament Research In pictures: Isis' weapons factories Stocks of French-manufactured Sorbitol, Latvian potassium nitrate and Lebanese sugar at an Isis weapons factory in Iraq Conflict Armament Research In pictures: Isis' weapons factories A destroyed Isis weapons facility in Qaraqosh, Iraq, November 2016 Conflict Armament Research

The 17 March strike sparked outrage in Iraq and beyond with calls from local government officials as well as the United Nations for greater restraint in the fight against Isis for Mosul. The United Nations reported nearly 2,000 civilians have been treated for trauma since the fight for western Mosul began in February following the formal launch of the operation to retake the city in October 2016.

Iraqi forces declared Mosul's eastern half “fully liberated” in January, but have since struggled to retake the city's western side. Claustrophobic terrain and tens of thousands of civilians being held by the extremists as human shields have bogged Iraqi and coalition forces down.

The US began the campaign of air strikes against Isis in 2014 after the extremists pushed into Iraq from Syria, overrunning Mosul and large swaths of Iraq's north and west. Since then Iraqi forces have slowly clawed back territory. Now a cluster of western Mosul neighbourhoods are the last significant urban terrain under Isis control in Iraq.