Mosul air attack killed at least 105, say US commanders

A US strike targeting Islamic State (IS) group militants in a Mosul building in Iraq in March killed at least 105 civilians when the blast caused IS weapons to explode, a US general said on Thursday.

"The secondary explosion triggered a rapid failure of the structure which killed the two ISIS snipers, 101 civilians sheltered in the bottom floors of the structure and four civilians in the neighbouring structure to the west," US Air Force Brigadier General Matt Isler said of the 17 March incident.

"An additional 36 civilians who are believed to be connected to the structure remain unaccounted for."

The United States has previously acknowledged that it "probably" had a role in the civilian deaths, but it has always said this was unintentional. 

According to Isler, Iraqi counterterrorism service (CTS) troops had been moving into the al-Jadida neighbourhood in west Mosul on the morning of 17 March when they came under fire from IS snipers hiding on the second story of a large structure, part of which was residential. 

CTS and coalition forces did not know civilians were in the building, Isler said, and ultimately a strike was called in.

The precision-guided bomb selected - a GBU-38 - was set up to cause only localised damage to the building, but it ignited a large amount of explosive material which IS militants had previously placed inside.

"Post-blast analysis detected residues common to explosives used by ISIS, but not consistent with the explosive content of a GBU-38 munition," Central Command said in a statement.

"Our condolences go out to all those that were affected," said Major General Joe Martin. 

"The coalition takes every feasible measure to protect civilians from harm. The best way to protect civilians is to defeat ISIS."

Later on Thursday, a monitor said US-led coalition air strikes killed at least 35 civilians in an eastern Syrian town held by the Islamic State group.

Head of the Syrian Observatory for Human Rights Rami Abdel Rahman told AFP that most of the dead were relatives of IS militants and included Syrians and Moroccans.