LONDON (Dispatches) -- A U.S. airstrike on the eastern Syrian town of Mayadeen early on Friday killed at least 80 relatives of Daesh terrorists, including 33 children, a monitoring group told AFP.
"The toll includes 33 children. They were families seeking refuge in the town's municipal building," said Rami Abdel Rahman, head of the so-called Syrian Observatory for Human Rights.
Earlier on Friday, the UN human rights chief called on all air forces operating in Syria to take greater care to distinguish between legitimate military targets and civilians in their escalating airstrikes.
A separate U.S. airstrike late on Thursday evening killed at least 35 civilians.
"The rising toll of civilian deaths and injuries already caused by airstrikes in Dayr al-Zawr and Raqqa suggests that insufficient precautions may have been taken in the attacks,” UN High Commissioner for Human Rights Zeid Ra'ad al-Hussein said in a statement.
Airstrikes in mid-May killed nearly two dozen farmworkers, most of them women, in a village in eastern Raqqa and at least 59 civilians in residential areas of Dayr al-Zawr, Zeid said.
A U.S. military spokesman told Reuters that American forces had conducted strikes near Mayadeen on 25 and 26 May and were assessing the results.
The Thursday evening airstrike in Mayadeen killed at least 35 civilians, including family members of Daesh terrorists, said the Observatory.
The deaths bring the total number of people killed in two days of aerial bombardment in Mayadeen to 115 said the monitor.
Residents saw reconnaissance aircraft and warplanes circling the city at 7.25pm local time before they fired missiles which struck two buildings, one of which was a four-storey block housing Syrian and Moroccan families of Daesh militants.
Daesh is losing ground in both Syria and Iraq under assault from an array of sometimes rival forces in both countries. Many of its terrorists who have retreated from other fronts are amassing in Syria's Euphrates basin area.
Between 23 April and 23 May the Observatory reported that at least 225 civilians had been killed in U.S. strikes.
On Thursday, the U.S. confirmed that one of its airstrikes in Mosul in March killed at least 105 civilians.
The U.S. bombarded a concrete building in Mosul’s western Jadida district, where Iraqi forces were fighting against terrorists, on March 17. The deadly aerial assault caused the building to collapse.
A Pentagon investigation found that a 500-pound U.S. GBU-38 bomb triggered secondary explosions from devices clandestinely planted by Daesh in the building, causing the structure to collapse.
U.S. military officials said 36 civilians were still unaccounted for. Local officials and eyewitnesses say as many as 240 people may have been killed in the U.S. air raid.
The death toll is one of the highest in the military camping led by the U.S. against what are said to be Daesh targets.
The U.S. and some of its allies have been carrying out airstrikes in Iraq since June 2014. They have done little to dislodge Daesh but have claimed many civilian lives and heavily damaged the Iraqi and Syrian infrastructure.