Monitors said hundreds of Syrian civilians were fleeing two jihadist-occupied towns near the Iraqi border on Saturday, after a series of airstrikes targeted buildings sheltering extremist fighters and their families.
Accounts from witnesses said airstrikes on the Euphrates River towns of Mayadeen and Abu Kamal began earlier Friday and forced large numbers of residents into the countryside. The Islamic State group controls most of the oil-rich border region, and reports from the scene said the families of many IS fighters were among the civilians fleeing for their lives.
Multiple reports from witnesses said the airstrikes were carried out by warplanes from the U.S.-led coalition that has been targeting IS positions in Syria and Iraq since 2014.
Pentagon 'assessing' reports
Monitors from the Syrian Observatory for Human Rights said at least 80 relatives of IS fighters were killed Friday, including 33 children. That report could not be independently verified, however.
The Pentagon has acknowledged there were coalition airstrikes in the region on Thursday and Friday. A spokesman said U.S. analysts were "still assessing the results of those strikes."
"We take all allegations of civilian casualties seriously," said Captain Jeff Davis.
Coalition airstrikes increasing
Earlier this month, at least 62 people, including more than 40 civilians, were killed in similar airstrikes at Albu Kamal, a border city once home to more than 40,000 people.
Apart from the latest incidents involving possible civilian casualties, the Pentagon said coalition airstrikes in Syria and neighboring Iraq have unintentionally killed 352 civilians since September 2014.
Analysts have reported an uptick in coalition airstrikes in both Syria and Iraq since the extremist group claimed responsibility for a suicide bombing in Manchester, England, that killed 22 people Monday and wounded more than 100 others.
U.N. plea: Protect civilians
In a related development Friday, U.N. human rights chief Zeid Ra'ad Al Hussein implored commanders on all sides of the long-running Syrian war to take greater precautions when attempting to distinguish between military targets and those that also may contain civilians.
"Unfortunately, scant attention is being paid by the outside world to the appalling predicament of the civilians trapped" in eastern Syria, Zeid said.
"Civilians should always be protected," he said, "whether they are in areas controlled by [Islamic State] or by any other party."