An airstrike by the US-led coalition killed at least 30 civilians on Monday in a Syrian town held by the Islamic State group on the border with Iraq, a monitor said. He says the victims were displaced civilians from Iraq and Syria.
The Observatory did not rule out that the death toll could rise as the wounded include several people in a serious condition.
He added that IS was using some apartments in the area targeted as local headquarters.
The Britain-based Syrian Observatory for Human Rights monitoring group said the strike hit the village of Akayrshi on Sunday night and that 12 women were killed.
Jones said Washington's information came from credible humanitarian agencies and from the US "intelligence community" and that as many as 50 people per day are thought to be hanged at Saydnaya.
It said the afternoon attack hit vehicles carrying farmworkers coming home from fields in the east of the province.
In its statement, Centcom confirmed that it had "destroyed an ISIS pump jack and an ISIS well head" near Abu Kamal and that it had fired nine strikes near Raqqa. He did not give an official estimate for the total number killed, but cited an Amnesty International report that between 5,000 and 11,000 had died between 2011 and 2015 in the prison.
Abu Kamal is a hugely important strategic holding of ISIS, though its value has dropped somewhat since they lost most of their territory in Iraq's Anbar Province.
US -backed and Kurdish-led Syrian forces are advancing on Raqqa after capturing several nearby towns and villages from the extremists, AP explained.
Human rights groups, however, say that the death toll may be much higher than reported as operations remain ongoing. A spokesman for the US-led coalition against Islamic State could not immediately be reached for comment.