The Syrian regime on Tuesday denied US accusations that it carried out mass killings at a prison and burned the bodies of the victims in a crematorium to hide the evidence.
"These allegations are totally unfounded, they are nothing but the product of the imagination of this administration and its agents," state news agency SANA quoted the regime's foreign ministry as saying.
Stuart Jones, acting US assistant secretary of state for Near Eastern Affairs, said on Monday that US officials believe the crematorium could be used to dispose of bodies at a prison where they believe Bashar al Assad's regime authorised the hanging of thousands of inmates during Syria's civil war, now in its seventh year.
"Credible sources have believed that many of the bodies have been disposed in mass graves," Jones told reporters at a briefing.
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 were thought to be executed at the Sednaya prison. The crematorium would be used to cover up the evidence, he said.
Amnesty International reported in February that an average of 20 to 50 people were hanged each week at the Sednaya military prison north of Damascus. Between 5,000 and 13,000 people were executed at Sednaya in the four years since a popular uprising descended into war, it said.
Assad's regime, Jones said, had detained between 65,000 and 117,000 people over the same period.
Jones said he was not optimistic about a deal to set up "de-escalation zones" inside Syria in an attempt to reduce violence and save lives. The deal was brokered by Russia with support from Iran and Turkey during peace talks in the Kazakh capital Astana earlier this month.
"In light of the failures of the past ceasefire agreements, we have reason to be sceptical," Jones said. "The [Assad] regime must stop all attacks on civilian and opposition forces. And Russia must bear responsibility to ensure regime compliance."