A report by the UN Commission of Inquiry said the US failed to protect civilians in an airstrike hitting a mosque near Aleppo in March. It also says the Syrian regime was behind more than two dozen chemical weapons attacks in the country.
US-led coalition forces failed to take "all feasible precautions to protect civilians" in a bombing on alleged terrorists near Aleppo in March.
The incident resulted in the deaths of 38 people and destruction of part of a mosque, UN war crimes investigators said on Wednesday.
"In one incidental attack, minutes before 7 p.m. on 16 March, a series of air strikes hit a building in a religious complex in Al Jina, killing 38 persons, including 1 woman and 5 boys," the UN Commission of Inquiry on Syria said.
The independent investigators, led by Paulo Pinheiro, said they were "gravely concerned about the impact of international coalition strikes on civilians."
"In Al Jina, Aleppo, forces of the United States of America failed to take all feasible precautions to protect civilians and civilian objects when attacking a mosque, in violation of international humanitarian law," the report said.
TRT World's Sara Firth has more on the story.
A US military investigator said in June that the air strike was a valid and legal attack on a meeting of Al Qaeda fighters.
It was believed to have killed about two dozen men attending the group's meeting and caused just one civilian casualty.
The American F-15s hit the building adjacent to the prayer hall with 10 bombs, followed by a Reaper drone that fired two Hellfire missiles at people fleeing, the UN report said.
"Most of the residents of Al Jina, relatives of victims and first responders interviewed by the Commission stated on that on the evening in question, a religious gathering was being hosted in the mosque's service building. This was a regular occurrence."
"The United States targeting team lacked an understanding of the actual target, including that it was part of a mosque where worshippers gathered to pray every Thursday," it said.
"Mosques are protected objects under international humanitarian law. Protected objects may not be made the object of attack unless used for military purposes, which would be the case if an Al-Qaida meeting, with regional leaders present, was in fact taking place," the report added.
TRT World's Alican Ayanlar reports from Turkey-Syria border.
Assad's chemical attacks
The commission also said Syrian regime forces have used chemical weapons more than two dozen times during the country's civil war, including in April's deadly attack on Khan Shaykhun.
A regime warplane dropped sarin on the town in Idlib province, killing more than 80 civilians, the UN Commission of Inquiry on Syria said, in the most conclusive findings to date from investigations into chemical weapons attacks during the conflict.
The weapons used on Khan Shaykhun were previously identified as containing sarin, an odourless nerve agent.
But that conclusion, reached by a fact-finding mission of the Organization for the Prohibition of Chemical Weapons (OPCW), did not say who was responsible.
The report said the regime forces "continued the pattern of using chemical weapons against civilians in opposition-held areas."
Declaring the incident a war crime, the report added that the regime's air force "used sarin in Khan Shaykhun, Idlib, killing dozens, the majority of whom were women and children."
In their 14th report since 2011, UN investigators said they had in all documented 33 chemical weapons attacks to date.
Twenty-seven were by the Syrian regime of Assad, including seven between March 1 to July 7.
Perpetrators had not been identified yet in six early attacks, they said.
The Assad regime has repeatedly denied using chemical weapons.
It said its strikes in Khan Shaykhun hit a weapons depot belonging to rebel forces, a claim dismissed by the UN investigators.
That attack led US President Donald Trump to launch the first US air strikes on a Syrian regime air base.
A separate joint inquiry by the UN and OPCW aims to report by October on who was to blame for Khan Shaykhun.
The UN investigators interviewed 43 witnesses, victims, and first respondents linked to the attack. Satellite imagery, photos of bomb remnants and early warning reports were used.