At least 65 people were killed and dozens wounded on Tuesday by a Syrian air force raid on a cattle market in a village in territory controlled by the hardline Islamic State, a monitoring group and a resident said.
The raid hit the main livestock market in Khansaa, south of the Kurdish-held city of Qamishli in northeastern Syria.
Syrian government officials were not immediately available for comment. Its military campaign against Islamic State is being waged separately from U.S.-led air strikes on the group, which has seized around a third of the country.
"The raids hit part of the market where traders from several towns and villages in the area traditionally bring their cattle to trade and sell in them livestock," said resident Khair al-Obeidi, who spoke by phone from the area.
"There are at least 65 bodies mostly charred bodies that were counted by local medics in Tel Hamees," he said.
One of his relatives was wounded, he added.
Several thousand Bedouin Arab traders and customers had gathered in one of the region's largest cattle markets.
An opposition activist in Hassaka province, Abdullah Bakour, contacted on Skype, said the Syrian air raid had been preceded by several raids overnight in the area that lies in the heartland of territory controlled by Islamic State, an al Qaeda offshoot which has seized tracts of land in Syria and Iraq.
The British-based Observatory for Human Rights, which tracks violence across the county through a network of sources on the ground, said the strike resulted in "tens of dead and injured" but did not say exactly how many had died.